The thing is that while visual is a niche genre, there's a nice little market for it that's existed for decades. And over time, an efficient system has developed for bringing baby bands along to being serious bands and delivering their product into the hands of those who crave it.
And it didn't happen by accident, the forces of supply and demand created this system; the fact that it's still in place is a testament to it's success and that bands still feel it's the best route to go or else they would be looking to do it another way.
Again, think about what going DIY entails: you have to get the money together for recording, you have to design the merch, you have to get the money together for printing merch, you have to make a website, you have to create and maintain social media accounts, you have to look into copy writing and publishing your music, you have to find or design album art, you have to correspond with venues, pay someone to distribute the CDs you just paid to have made, etc etc etc etc. At the very least you're going to have to hire a booking agent and manager, and if you don't want to do all of the above stuff yourself, you're going to have to pay someone to do it.
So you're going to have to put up loads and loads of money. And if you aren't wealthy, you're going to have to work all the time to pay for this stuff. When are you going to have time to write? Or practice?
In a fiercely competitive scene where lots of bands are offering the "same" product (visual music), and the music DOES matter, the band that has an label doing all the legwork for them (and has an optimized system for doing all this efficiently/low cost) while they just write music, practice, and chat with fans online all day is going to have a MASSIVE MASSIVE advantage over bands that don't.
So, despite some horror stories you hear, VK bands still think the "traditional" route to success is the best way to go at the moment.