Why did Pausanias travel to Greece?

Short answer

Pausanias does not clearly outline his aims in his work Periegesis or, if he did, that part of text has been lost. Thus, historians have had to rely on clues in Pausanias' text and what we know of the environment in which he was brought up. Looking at your list above, we can (mostly tentatively) surmise the following about his reasons for travelling around Greece and writing about it:

1. Tourist - part of his reason but certainly not his main purpose.
2. Pilgrim - to some extent, probably yes. He focuses a lot on religious buildings and mythology.
3. Family reasons - there is no evidence for this. In fact, we know nothing of his family.
4. Commercial - Pausanias was certainly eying potential readers (both real and armchair travellers) but there is no evidence for a commercial motive. In fact, he appears to have been independently wealthy.
5. Ordered by the state - very unlikely. There is no evidence for this; in fact, we are not even sure from where exactly he hailed, though Lydia (part of the Roman province of Asia) seems very likely. Pausanias spent around 20 years travelling and writing and seems to have been the sole arbiter of what he wrote about and how the work was structured.

There is also no evidence that his work was commissioned, and it seems highly unlikely given how many years it took Pausanias to write his ten volumes. It is far more likely that the reasons for his travels (in addition to some of the points on your list) were to preserve and share knowledge of the past, and to satisfy his own yearning to see and learn about the rich heritage of mainland Greece.

Details

On 'knowing' Pausanias the man, Maria Pretzler succinctly outlines the problem:

Pausanias is notoriously elusive: he does not provide much information about himself, and little can be said about him for certain, at least if we are merely looking for hard facts about the man behind the book. What we know about his personality also has to be pieced together from sometimes contradictory statements in the Periegesis [Description], combined with conjecture based on an assessment of the cultural context.

Source: Maria Pretzler, 'Pausanias: Travel Writing in Ancient Greece' (2007)

Modern historians have written much on Pausanias' possible reasons for his travels and on what his aims in writing Description were. Although he does not focus exclusively on the classical and Hellenistic periods, there is a consensus that an important aim was to preserve knowledge of those periods. His work (and motives) has been compared to Herodotus in that

Apart from the common Ionian, restless spirit, the two writers through their work desired to commemorate human deeds and especially important manifestations of the Greek ideology and culture both in theory and practice. In order to serve this ambitious goal, they both collect their material by autopsy, by oral or written sources and make their final selection, interweaving history with folklore, mythology, geography, art history, ethnology and ethnography.

Source: Pitropou Ekaterini, 'Wandering as the Determinant of Identity and Difference in Ancient Greek Literature: The Paradigm of Herodotus and Pausanias'. In Vicky Katsoni (ed), 'Cultural Tourism in a Digital Era' (2015)

Other historians have also made this connection with Herodotus. More specifically on Pausanias, and under the heading Pausanias: A Nostalgic Traveler of Roman Times, Ekaterini adds:

He was a mythographer, a geographer, a pilgrim, a historian, an art historian, a travel writer....As a romantic and nostalgic traveler of Roman times, his aim is to compose a special travel guide that would present and thus preserve, through with accurate descriptions and explanatory narrations, all that is worth seeing and commemorating.

"Map based on Description of Greece by Pausanias. The map shows which parts of Greece each book in the work describes." Text and image source: 'Pausanias' locations in his Description of Greece' (Ancient History Encyclopedia)

Pausanias was, in a sense, an academic, and he sought to educate both himself and his potential readers on, in his own words, "all Greek matters". He also came from a region which

produced writers of all sorts in greater number than mainland Greece.

but it was

mainland Greece [which] had the greater authority as a repository of Greek tradition and as a living monument to the Greek past.

Source: Ewen Bowie, 'Inspiration and Aspiration'. Chapter 2 in S. E. Alc**k, J. F. Cherry & J. Elsner (eds.), 'Pausanias: Travel and Memory in Roman Greece' (2001)

Ewen Bowie (Professor Emeritus of Classical Languages ​​and Literature at Oxford University), who contends that the evidence strongly suggests that Pausanias came from Magnesia ad Sipylum in Lydia, further argues that

Pausanias’s Magnesian origins may have directed him to literary activity more firmly than would upbringing in any city of mainland Greece other than Athens; and they may have enhanced his fascination with the past of a mainland Greece to which he was a visitor and in no city of which he was a native.

Sadly, despite Pausanias' clear desire that his books would find an appreciative audience, it seems that Description was not widely read in ancient times. Also, it was also poorly regarded by many classicists of the 19th and early 20th century. While there is some room for criticism of Pausanias' literary style, as well as some obvious errors, the overall value of the text far outweighs these shortcomings, particularly for archaeologists.

Other source:

Christian Habicht, 'An Ancient Baedeker and His Critics: Pausanias' "Guide to Greece"'. In 'Proceedings of the American Philosophical Society, Vol. 129, No. 2 (Jun., 1985)'