Honestly you probably just explained why there won't be a Lego Mario Bros game. 

Well that and Nintendo doesn't really need another studio to make adventure platformer games that are kid friendly. They do that themselves and earn more per unit than they'd get via contracting Lego to do it. Its not like, say, Mario Rabbids where it is a very different genre and take on the idea, for example. 

LEGO games arent adventure platformer though - or at least in the form that is similar to Super Mario, DK or Kirby.

And there's no agreement that LEGO games need to be Multiplat - this is probably Sony giving the greenlight (and a bit of a middle finger to Xbox lol).

Mario Rabbids, Hyrule Warriors, Fire Emblem Warriors, Pokken Tournament, Cadence of Hyrule, Pokemon Mystery Dungeon, and Tokyo Mirage are all developed by third parties and have all the games exclusive to Nintendo platforms.

No need, happily play them on PC

That's what great about Nintendo the hardware is so easy to emulate. Ps3 came out in 2006 and switch in 2016 and emulation on Switch is vastly better.

What's interesting is this actually seems to be developed by Guerrilla themselves, which should not only bode well in terms of it being both well made and faithful, but means this will be an internally developed Sony game on Switch.

If it's releasing on Switch it might as well release on PS4 too to maximize sales potential. Horizon Forbidden West also released on PS4.

Skipping PS4 but still releasing on Switch is an interesting choice; perhaps by now Switch's active userbase is just that much bigger than PS4's that they figured it was worth it for Switch but not Sony's last gen machine; this has happened with a few games now such as The Plucky Squire, Tales of Kenzera Zau, Penny's Big Breakaway, Mortal Kombat 1, the Dragon Quest III remake, Nikoderiko, etc.

It differently interesting but I won't count on Sony releasing there system sellers ip on switch. This is gonna do much better on Switch then ps5 imo, if Sony releases god of war of zero dawn then that would be a radical shift for sony.

Yeah I don't expect the big stuff like God of War or mainline Horizon to come to Nintendo, at least not in the near term. 

I do think this could potentially set a precedent for less high profile stuff to make the jump in the future though; like how Microsoft brought Grounded and Pentiment to Switch/PS. True and complete exclusivity is growing increasingly rare in today's market as dev costs rise.

This does make me wonder if we might see Switch 2 have some port of say, Horizon Zero Dawn, Spiderman PS4, Miles Morales, or GoW 2018 on it. Honestly I think they could probably get Forbidden or Ragnarok to run on it via the PS4 versions as a base, but if they are only deciding to do it now they might see it as better to work on Switch 2 versions. 

..Though that would be a world, wouldn't it? 

Honestly something like this probably costs a lot less than the above titles to make, even with Lego fees. But if you need to sell, IDK, 12 million units of the next Horizon game to break even, it might be considered profit efficient to port the earlier games to Switch 2 for both more cash flow and advertisement.