Because:

# They make their money selling those things.
# They have different teams working on different things.
# You don't just slap a new thing in the game without testing, other than betrayal of course.

lol PoE repeatedly puts things in untested/undertested. They always have and always will and that is fine because they acknowledge the problems usually fairly quickly and work on fixing them.
As soon as they released this unique tab and the community let them know how much it sucks Chris posted himself that they didn't realize many of the issues with it and are going to work on making it useful. As it is; its not even useful to collectors who is the sole target of this tab.
I highly doubt they have different teams working on developing stash tabs. That would be asinine to say the least.
And if its about making money they would make a ton more with a delve tab which has much higher demand and player interest than a collectors tab.

why pay staff to test content, when u can release update and have players test and complain about broken stuff for free XD

Stupidest thing on the list. GGG even forgot how to make money. Its almost as it they dont want people to flip delve items and make real money easier, or get rich in the game easier. But that cant possibly be true, because everyone has at least nine mirrors now because of betrayal. God are these people stupid.

i have a full tab of purple breachstones which i wont use cause its so pretty like this

that and you can't run them.

Better off flipping the drop rate has been butchered over and over again. Especially chayula.

but but but...its purple ! cant sell!

bad tab

i'll laugh if it has the same bugs as the map stash tho