https://www.citynews1130.com/2019/07/19/suspect-in-animation-studio-arson-fire-reportedly-had-grudge/
As of this time, it has been figured out that he was not an employee of the studio nor was he an otaku of anime (trains, he was though). He says that he believes they stole novels and people are sure they heard "you ripped me off" among other things. Not sure what that's referring to, but that's his claim.
The reason that there are so many deaths is because the killer blocked the exits, so it wasn't just because it was an older building at fault, but this man did everything possible to kill everyone.
There are 33 people who have died, 37 are in the hospital (some still in critical condition who may die), and everything that Kyoani has ever done has been lost to the fire.
Regardless of campaign to give back to KyoAni to help those who survived this tragedy, this is probably the end of Kyoto Animation. I'm just hoping that those who survive are able to live to their fullest.