Upvote:3
Formally the sole difference when applying for a 2/5/10-year visa is the higher fee. However, the GOV.UK website does state it's meant for those who "need to visit the UK regularly over a longer period".
As such, besides having sufficient clean travel history in the UK (visas/stamps, including in previous passports), one should provide evidence of ties to the UK motivating frequent visits which are nonetheless visits. It is even more essential than in general to prove one will get by without resorting to employment/public funds and that one has compelling ties to the country of residence. Proving ties to home and sufficient ties to the UK to motivate frequent visits won't be the easiest of tasks for many.
As such, a multi-year visit visa simply isn't for most people.
That said, just because they don't grant a multi-year visa doesn't mean you'll be rejected altogether, but you won't be refunded the fee difference if issued a shorter-validity visa.