Probably to stay on top of exploits
Ah the Wii U: the forgotten system. It’s even passed up by the Let’s Sing franchise (two years running!) in favor of a Wii release. That’s W-I-I, as in, the 2006 system. It hasn’t been updated since July 2017, several months after the Switch started dominating headlines, but Nintendo saw fit to give it a quick tune-up this week. It was more of a lateral move.
Nintendo dropped one of its classic “system stability and usability” updates on us for the Wii U, bumping the firmware up to 5.5.3. It’s sort of significant in that Nintendo is at least willing to ensure that there aren’t any piracy-related vulnerabilities on the thing (it is still selling games actively off its eShop after all, and many Switch games are almost carbon copy Wii U ports), or patching up legitimate bugs.
All hail the Wii U. I still use it!
System Menu Update History 5.5.3 [Nintendo]