Revolvers are simple, which makes them reliable. The bullets don’t feed so they can’t jam up like they can in a semi-auto pistol. You can drag a revolver through the mud and chances are the cylinder will still spin well enough to shoot it. By comparison, just using cheap ammo and/or not cleaning your gun often enough can often cause a semi-auto to misfeed and jam.
A revolver will also fire a wide variety of rounds, basically anything that fits in the chamber. A semi-auto sometimes won’t cycle properly with low-recoil rounds and is much more picky in general about the size and shape of the ammunition. If you want to fire more or less powerful rounds in a semi-auto reliably, you can tune it to do so by adjusting springs and such, but a revolver just fires them all, no problem, no adjustments.
A double-action revolver requires a somewhat hefty trigger pull, so they aren’t as likely to have an accidental discharge as a semi-auto.
Being simpler, they are less expensive.
Being simpler, they require less training to learn how to use one properly.
Snub nose revolvers are pretty dang small, and are therefore easy to conceal.
Revolvers have their disadvantages as well.
A revolver typically holds 5 or 6 rounds, and for safety you often want to leave one of the chambers empty so that if the hammer catches on something it won’t snap down and accidentally discharge. Semi-auto pistols tend to hold more rounds per magazine, with somewhere between 9 and 15 being common.
Revolvers are slower to reload, though there are quick loaders out there that load pretty much as fast as a magazine for a semi-auto.
While the lighter trigger makes semi-autos more prone to accidental discharge, some people also see the lighter trigger as an advantage, making the weapon easier to shoot in some ways.
It’s a bit easier to fire a semi-auto quickly. If you need to do a spray and pray type of thing, a semi-auto sprays faster and sprays more lead before needing to reload.