Aside from finance, a big motivation to buy a home in the UK is to have more self-determination in your home life. Renting places you under someone else's control to a large extent.
You often can't decorate much. Can't fit better windows, and windows where I've rented have usually been poor quality. Can't replace the washing machine even if it's not working properly. Can't put up shelves.
Can't fit solar panels or better insulation, or replace carpets. Sometimes you can't even paint the walls.
In the town where I live nearly all rental properties are "furnished", to the point that there aren't many unfurnished properties to choose from. This means you can't change the furniture - couches, tables, curtains (drapes), beds, wardrobes etc. Often there is an old TV you would never choose for yourself. Of course you do make some choices when you decide where to move into, but there may not be anything particularly to your own taste, and what you want will change over time anyway.
Aside from the lack of self-determination while in there, there is a constant threat of "no reason" evictions which landlords exercise from time to time. Because no reason is given, it doesn't take much. I've seen it done sometimes by rental property agents just so they can advertise a large rent increase on the open market which would not seem reasonable applied to the existing tenant - that time, the landlord didn't particularly want the tenant out, but the agent saw a chance to get their new-tenancy fees and advised the landlord to evict.
Long term stability in a rental property is a luxury in some areas, and finding another property nearby may not be possible. Got a child in school? Don't assume they will be able to stay in the same school.
I have encountered rental situations where it is required to pay 12 months rent up front every year during the tenancy (on top of 1.5 months deposit) - but only if you're not well off enough to qualify for monthly rental payment. This sucks if the reason you are moving is because of a no-reason eviction from a previous place, so you quickly need to find another property as well as 13.5 months worth of rent at short notice. Naturally, you can't use the deposit from the previous place in that scenario as you won't get it in time, and you won't get all of it.
Speaking of 12 months, in the town where I live and I gather in many others, 12 month tenancies are the maximum you can get. Technically every year there's a new tenancy, usually with new contract fees to pay, and the possibility they might decide not to renew it. If you're really unlucky there might be a new credit and income check each renewal, which you will fail if you fell on hard times, such as between jobs. This duration is because UK law has additional tenant protections with tenancies longer than 12 months. So of course landlords don't offer them.