It depends on what games made him love those systems. I just assumed they were mostly Nintendo ones. :L

This.

Can never forget the first time i played megaman and megaman x! Also love my street fighter, super  mario world, DK and star fox on SNES!!

If Nintendo were 3rd party I would buy a decent amount of ninty games

I genuinely mean this in a non trollish way... but I feel I grew out of Nintendo from back in the Super Nintendo years. The 1st party games don't do it for me anymore.

I compare it to my love for Assassin's Creed. Amazing at first. Now I can't even get into it at all.

Love Nintendo, never going to give up on them

The only thing I would say about this is that there are a variety of Nintendo 1st party games.  The thing that makes a Nintendo game a Nintendo game isn't the way the game is played or what kind of mechanics it has.  

Of course, I imagine that when you say you "grew out of Nintendo," you don't mean maturity-wise since it makes no sense that way.  

Perhaps your taste in games have changed, and it probably has to do with artistic direction as well (since many Nintendo games share this aspect).

Pretty much a Nintendo guy at this point.

I dunno, I'm mostly speaking through a consumer stand point right here, having to go through an extra paywall just to play game that could've been done in other machines doesn't sound appealing in the slightest. Also, it kinda already is a Monopoly, Nintendo making hardware is doing little difference in the home console department right now, and has been doing little to no difference since the 2010's started.

Not from a handheld perspective. 

I clearly said "in the home console department". :P Let Ninity retain their Handheld crown for what it lasts, while they make console games in normal hardware.