Yeah a game at 2 mio sold units for the predecessor, sold bundeld with the first game for moderate price, which got marketing like: cosplay in playboy magazine and tv commercials cant compete with a new ip which got a kids/squid advertisment. okay.

Biggest Bayo2 tv commercial on youtube: https://www.youtube.com/watch?v=rH0OsWgJeyw

1,4 mio views; 99% positive rating

Biggest Splatoon commercial on youtube: https://www.youtube.com/watch?v=pjPOSKnOftA

1,4 mio views ; 48% positive rating

Both game had the same range. Dont try to find excuses that dont exist. Splatoon sold that good because its cartoony and rated e. Most wii u Owners are kids and they dont play realisitc looking rated m games.

The Deus Ex: HR, Watch Dogs, I will throw in the ports of Mass Effect 3, Tekken Tag Torunament 2 and other third party games put on the Wii U were all late ports. Extremely late as in more then a year after the original release in some cases. While there were some that arrived on time, in today's gaming world, no one waits for late ports aside from the hardcore PC gamer that doesn't want to get a console.

I do agree that some of the titles that were released multiplatform at the same  time and didn't get much love but given how some companies refused to make DLC available for their Wii U efforts and pretty much most declared before 18 months were up they were giving up on the system while still supporting titles on the PS3 and 360 along with their PS4 and Xbox One counterparts, it is hard to say they didn't have anything to do with the Wii U's struggles.

All that being said on the main topic, 3rd parties can be reasonably successful on the Wii U by making decent games that are exclusive to the platform. You saw some of that in the Wii era before most gave up because they weren't getting COD type numbers on the platform for certain genres. Which is funny because when making games on other platforms they still never got the COD type of numbers they seem to have been aiming for. But all that being said, giving some exclusive support on certain titles that would appeal to the Wii U's traditional following would have netted them some good sales.

People talk about install bases but the key to these bases are actually built on the premise of there being a foundation. For about 4 generations now outside the early portion of the Gamecube life cycle, there hasn't been a lot of solid 3rd party support on Nintendo consoles outside of ones that we sell now like Skylanders and Just Dance.  Many of the 3rd party exclusive games you can say were classic usually wound up being ported, under supported in terms of features compared to other system (although whether that is third party developer's effort or because of the system and structure varies from game circumstance to game circumstance) and overall one can make the excuse it is because Nintendo fans only want to play Nintendo games but you could also say it is because they just don't trust other publishers/developers due to prior experiences on previous Nintendo platforms.

Time will tell if this changes with the NX but no one party or group is solely to blame for 3rd party issues on the Nintendo Wii U

The game sold 2 million units across two consoles that had "hardcore" reputations and had a combined install base of 100+ million. The second game sold 600k on 10% of that install base. Bayonetta 2 had ads but not as much as Splatoon. You rarely see Nintendo go as far as they did with Splatoon.

The commercial getting the same amount of views on YouTube doesn't change the fact that Bayonetta is a niche title, and what do the positive ratings on YouTube have to do with anything?