You're right, but it goes beyond that.
Yahoo used to be a titan. I was a regular user of Yahooligans back in the day. Yahoo (at one time) had been my go to search engine. I can't say that it was ever my primary email account, but I used it. I used Yahoo Messenger. I was part of a community that centered around some Yahoo games. Yahoo used to be a titan that was a direct Google competitor in the realms of communication, search, news and entertainment.
Sure, I can delete an account for any service belonging to any company(!) if I want. But when you use a service, there's an explicit level of trust that they'll protect your information to the best of their ability. We assume that we can use their services as our primary driver without worrying about MD5 hashes without salt. We assume that they'll take more security procedures than a student making a toy app testing boundaries in a 400-level course.
Sure, we can delete our account, but this is an unnerving situation. It's not like Yahoo was thought to be some back alley operation where everyone nervously awaited news like this. Yahoo was a direct competitor and contender to some of the biggest digital companies on the Web. This level of incompetence is mind blowing.
At least it is to me.