They do their job well? Hm..All the arguments of 'glitches/testing/etc' would be acceptable is Nexon were a startup company,It's 13 years for KMS and they do their job well. For GMS, it's been 11 years and they do not do their job well. Remember that KMS is where most of the features come from.
The problem is, any and all patches/updates generally lead to fixing one problem and creating 4-XX more issues ... from a company 13 years into their own game and still, causes more problems than repairs.
Over time, you are supposed to get better at your trade, not worse.