Tor and VPN are two different things, this question doesn't make sense It's like asking someone why they use the gas pedal in their car when it also has a brake pedal - why wouldn't you use both to have a useful car instead of a brick?
There are lots of takes on what makes good privacy. Some think tor makes you stand out and orbot has leaks. Many VPN are surely not doing what they say. I like to run onion instances so I use it. But I understand there is no perfect privacy. More interested in learning about how to use things.
If the point is to hide your IP from relays then running your client through a VPN and then through tor (or vice versa) is redundant and unnecessary. maybe there are other reasons to do so but thats the usual idea.
A VPN doesn't hide traffic from your ISP like a brake pedal doesn't make the car go fast
but it does tho. and also thats really weird inaccurate simile.
I guess there are different ways to set up a VPN to hide traffic like there are with Tor but it seems more straightforward and reliable with Tor and most VPN users don't do it Not to mention all the other tracking services like Google
the main difference is that a VPN is a trusted 3rd party TOR Isnt (mostly) so if you have reason to doubt your VPN or are doing high risk activity, definitely use tor. but many people are betting that the mullvads and ivpns etc are secure. not sure what you mean about configuration problems.
I just don't know how to configure a VPN to be hidden from the ISP, whereas in Tor browser (not sure about Android apps) it's easy