At the absolute minimum, MUT daily / weekly challenges and Play Now Live games are single player affairs, and those get tested before they are made live in the game as to ensure the rewards are delivered to users who win those challenges.
More likely it's because that bug in particular didn't cause a crash or any in-game instability, so it was flagged as a non-blocking and low-priority bug (i.e. it isn't a showstopper which should halt the release of the update), therefore it was reasonable to schedule work to fix that bug for later.
There are always perfectly reasonable explanations which are more likely than "EA is lazy" once you understand and appreciate the process of making a video game. There is a method to the madness, as it were.
I've been over this before but I'll say it again: y'all seriously don't give the people working QA departments enough credit. QA people are some of the hardest-working and most dedicated people in the industry, despite having some of the most brutal and thankless work thrust upon them.
EA and other AAAs are all serious about their QA process. That said, QA doesn't magically fix everything, particularly in a live service product with routine releases with hard deadlines which can't move. Stuff breaks. It sucks, but it's a fact of life. Humans aren't perfect. Let's be understanding here.