I dunno, people say "oh just the old stuff" at first, but then what about next yr and the yr after that?,. What happens when you've got all the "old stuff"?, naturally you're going to ask for the new stuff, so why not cut to the chase and just say "drop your console and release them all on Switch"?

It's like, over the course of this gen, the same question (veiled answer more like) has been asked in various ways, but it always comes down to MS just putting in the towel, to appease another console platform.

I always suspected that that was what they were trying to do the last time but didn't manage to convince Nintendo at the end.

Greenberg already said, "We have no plans to expand any of those exclusive first-party titles to any other consoles." This was right before Ori released on Switch. You also have to remember, Ori, Cuphead, and Super Lucky Tales are all from 3rd party developers. The only 1st party IP on other platforms is Minecraft.

I'd rather see Nintendo's games on PC.

They are great games, providing millions of more gamers the potential to pick up and play those titles would be a good thing I think.

No I wouldn't. I actually thought that plus Rare games would have come by now.

I highly doubt they would. Probably in exchange for some IPs. MS release patterns tend to favour the smaller budget style games.

Is it really so hard to go out and buy the platform its made on?

It really isn't but sometimes you gotta "Ttojan horse" then to get them to even try your product.

Sucks that it's not an Nintendo IP to begin with,the killer instinct on the SNESS was one of my most beloved fighting games together with Street Fighter 2.

Honestly I don't really get the OP's main premise that porting Halo to Switch would somehow gain Xbox customers.
You already said a good majority of Switch customers also own one of the big 2 consoles.
Having Halo or other major Xbox IPs on Switch isn't going to make Xbox attractive to somebody who hasn't been attracted to them.
If a customer is inclined to like Halo or these other games, they probably already play it and own an Xbox.
So the big strategic play angle seems dubious. That said, you can say MS can target Xbox/Switch crossover audience
to sell more games to them in most convenient format/location, which sounds plenty reasonable to me.
I honestly wouldn't limit it to just "ports" but more platform-optimized new games building on same IP/genres.
That could even recycle elements of old games, but twist in new ways... Some boardgames do this with multiple rulesets.