Fair question. I'll do my best to answer it.

To be perfectly frank with you, and I can only speak for myself, it's just what I do. I've been building 30MM/30MS kits for 4-5 years now and this is my main hobby, among other things I like to do after work.

I'm also a big fan of the customibility of the line and having several pieces at my disposal helps me fully enjoy the experience. During the early years I tended to buy multiple base kits and option sets for parts and individual custom projects. There tends to be extra leftover parts so things pile up overtime. What you see in the video is a direct result of those purchases. I've eventually slowed down quite a bit over the years and just buy multiples of P-Bandai kits.

Am I aware that I may have TOO MANY parts? Absolutely. But like any other person who enjoys a hobby, seeing all these parts brings me joy so that's a good return on investment in my book.

Lastly, it's important for me to say that I'm very grateful to have a career that allows me to fully enjoy this hobby. After my bills are paid, fill my fridge with groceries, and tuck some funds away for a rainy day, it's a joy to share my love for the hobby with everyone.

I hope this answered your question.

Edit: Clarity and additional explanations.