The two main reasons to use your own router are cost and security. Internet providers tend to charge you a monthly rental fee which you can avoid by having your own equipment.
The other is security. Having your own router prevents a provider installed backdoor being used to get into your network. The number of times magic passwords have gotten into the wild is not zero, so is the number of times vendors have allowed zero-day exploits to go unpatched. .
There’s also the matter of features. For instance, if you wanted to use a mesh aware router, Wifi 7, etc.
Just make sure to set your router to auto-update to ensure any future security holes are patched and you’ll be fine.
Right now the bargains in Wifi routers are Wifi 6 capable unit which are being discounted now that Wifi 7 is out. They'll serve you well for many years.