Were different parts of the Pali Canon intended for different audiences?

In the first council collect Dhamma(suttas) from those who have listened from the teacher and check for correctness. After that group them as DN - Long, MN-Middle and (KN) Shorter ( Books) collections. Also some suttas group according to topics base in SN. In AN group in numerical base of topics for easy reference.

Purely subjectively, to me, it looks like DN suttas are rather artificial compilations, followed closely by MN suttas.

Of these two DN suttas seem the most contrived - none of them look like Buddha's direct words to me but rather like nice and clear summaries assembled from Buddha's quotes with some glue added for smoothness.

Samyutta and Anguttara Nikayas are very different from the above, esp. Anguttara feels like an anthology of raw quotes as close as it gets to Buddha's own words.

My speculation is that Nikayas were created not with specific audiences in mind, but rather by following four very different methodologies. Perhaps DN were created as all-encompassing summaries of the entire teaching across wide range of Buddhist topics, by people who believed that the raw unedited teaching was too fragmented and incomprehensible to most people. MN was seemingly made by picking the points that were most often debated by the non-Buddhist sects and creating nice clear arguments against them. SN feels like a result of an enormous effort to organize the quotes by topics, by people who must have believed in the power of reason. AN seems like a simple collection of all kinds of quotes by rather practical people who believed in K.I.S.S. (keep it simple, stupid). KN is various useful and not-so-useful Buddhist folklore that is not made of Buddha's quotes.

Naturally, the methods and attitudes of the compilers reflected in the suitability of this or that collection for certain audience. But I don't think they were specifically intended for different audiences, no.

In addition to what @RobM has mentioned.

There are 4 types of learners¹:

1. The intuitive or quick learner (ugghatitañña)
2. The intellectual (vipañcitañña)
3. The one who needs guidance (neyya)
4. The rote learner (pada,parama)

There is a view that the Abhidhamma is for the type 3 & 4. Type 1 & 2 have realised a lot due to their past pratice and a Sutta would clear the dust in their eyes. The ones who need more learning are 3 and 4 hence have to lean the doctrine. The Suttas are like a collection of prescriptions given to cure a particular person. The Abhidhamma contains the complete doctrine or the body of knowledge medicine. You become a doctor or knowledgeable in medicine by studying the body of knowledge of medicine and not my reading prescriptions. Also if you are a medical intern you might sometimes need guidance from a doctor. (Guidance coming from the Suttas). Your current knowledge base from past pratice and study to become an intern. (Comparable to the Abhidhamma) Moreover, type 1 & 2 just listening to the Sutta realised the Dhamma from their past pratice type 3 & 4 need to learn the full doctrine hence rely on the Abhidhamma.

This is just a view held by some.

¹ To read more on them see: Levels of Learning by Piya Tan

Bhikkhu Bodhi, in his introduction to the Saṃyutta Nikāya:

Prevalent scholarly opinion, fostered by the texts themselves, holds that the principal basis for distinguishing the four Nikāyas is the length of their suttas. Thus the largest suttas are collected into the Dıgha Nikāya, the middle length suttas into the Majjhima Nikāya, and the shorter suttas are distributed between the Saṃyutta and the Aṅguttara Nikāyas, the former classifying its suttas thematically, the latter by way of the number of items in terms of which the exposition is framed.

However, in an important groundbreaking study, Pāli scholar Joy Manné has challenged the assumption that length alone explains the differences between the Nikāyas. By carefully comparing the suttas of DN with those of MN, Manné concludes that the two collections are intended to serve two different purposes within the Buddha’s dispensation. In her view, DN was primarily intended for the purpose of propaganda, to attract converts to the new religion, and thus is aimed mainly at non-Buddhists favourably disposed to Buddhism; MN, in contrast, was directed inwards towards the Buddhist community and its purpose was to extol the Master (both as a real person and as an archetype) and to integrate monks into the community and the practice. Manné also proposes that “each of the first four Nikāyas came about in order to serve a distinct need and purpose in the growing and developing Buddhist community”.