1) Excellent 1st and 3rd party support
2) great prices for games, both physical and digital formats
3) Variety, you can find games for almost all genres.
4) They are consistent.
I know that fans from other companies will say that it’s because the other console manufactures screwed so bad and blah blah, but even with probably the worst launch in history like the PS3 (high price, complexity of the hardware and many more) Sony managed to sell 88 million units worldwide.