One big benefit of making your own IR’s is you know exactly what’s been done to make them, and you can easily verify that they’re doing what they’re supposed to. If you want accurate (rather than ones you like the sound of) IR’s then you really have to trust the person making them is making the right calls.
I don’t think it’s hard to do, but there are pitfalls to watch out for and some people make certain judgements on balancing various compromises that I don’t always agree with. It’s somewhat similar with making amp captures, I really just feel more comfortable making and using my own.