While your initial drills start out using relatively few rounds at a time, more complex/difficult drills involve far more rounds, often requiring multiple magazines and multiple targets. These types of drills are generally aren't done at your basic indoor shooting galley ranges but even there there are plenty of ways to burn through a substantial amount of ammunition.
And while part of it is that in general shooting as a hobby is fun, another part is that some types of drills just require a lot of ammunition. ex: malfunction clearing drills where there are non-functional rounds mixed in to your magazines and you need to perform your drills with as little time loss compared to normal as possible. i.e. knowing how to react when things go wrong under pressure.
And so a single range day can easily put someone through tens of magazines which quickly gets into the hundreds of rounds. Then assuming you are going to the range weekly, biweekly, or monthly, that puts you into thousands or even tens of thousands of rounds per year.
If ammunition didn't cost what it did, I'm sure I would shoot a lot more.
I think it’s possible for many shooters to achieve parts of a flow state when doing this. Imagine the satisfaction of throwing, catching, or hitting balls over and over in muscle memory, letting your mind and body work together to let your coordination and accuracy improve to solve the puzzle.
Now at $.25-.$30 / round, this does add up to an expensive hobby.
I’d estimate I have shot over 100K rounds of 7.62 thanks to a good amount of time as an M60/M240 Gunner
This is part of why "gun people" roll their eyes when the news talks about someone "hoarding thousands of rounds" - it's no where near as much as you might think, and people like to buy ammo when it's on sale (ammo's expensive!).
I should have clocked tens of thousands of rounds by now, at least one order of magnitude larger. Especially since micro-pistols like the P365 need the user to be more consistent with training, given that it's more difficult to be accurate with than with a full size gun. But life happens and I need to readjust my priorities before I get back to consistently visiting the range again.