What is A and B games in your opinion?
To put it simply, it's the games Nintendo makes vs almost everything else 3rd parties, Sony and MS make.
Nintendo has the kids/family/8 to 80 years old oriented games like Mario, MK, Smash, Zelda, Yooshi, Kirby, Animal Crossing, Pokemon. The others have the Halos, Gears of War, Destiny, Call of Duty, Uncharted, Forza, Gran Turismo, Killzone, God of War, Bloodborne, etc., etc.
The problem is that MS and Sony have the majority of their 1st party or exclusive library focused on those kind of games/genres. Nintendo does not.
And when in the past, being Nintendo was OK because there was demand for those games or 3rd parties did make games like those. Now they don't. They changed and the market changed. Only Nintendo didn't. And now you can see the result.
It does hurt Nintendo even more that kids can be just as happy with their smartphones or tablets playing those free or really cheap games. Why will parents bother so much buying a console and games when they can lend them their mobile devices and download a free game?