I don't really think that Nintendo is really reclusive and protective (well they are protective, but not for the same reasons you are suggesting) with their IP's, rather the problem is that they have too many good IP's that it may not be worth it to regularly use old IP's. I mean you have your big 3 that won't ever die with Mario, Zelda, and Pokemon; that see multiple releases/spin-off's every generation and get advertised like crazy, essentially their "lifeblood". And then you have the regulars (the series that at this point will regularly get new releases unless they start flopping like crazy), with things like Fire Emblem, Donkey Kong, Metroid, Xenoblade, Kirby, Splatoon, Animal Crossing, and Smash. And then you have them developing/co-developing new IP with Astral Chain, Dragalia Lost, Ring Fit on the side. On top of that, even if you hate it; there are spin-offs regularly released, just that most of them are on the mobile environment.
All of those largely cover pretty much every niche they could really want, and have a lot of room for potential growth. Just those alone give Nintendo the strongest 1st party lineup in the industry.
But then there are the underutilized series like Kid Icarus, Golden Sun, Star Fox, F-Zero, etc. And outside of Golden Sun and Kid Icarus, the gameplay loop of Star Fox/F-Zero is a hard sell for most people for a full price. Golden Sun could obviously be revived as a turn based JRPG, which has a lot of fans in the modern era. Kid Icarus worked really well with the split between on the rails and ground sections, and could develop more along that line but at the same time Uprising was a pretty good "sendoff" to the series, and outside of a port I don't really think it needs anything currently (and Sakurai is too busy with Smash anyways).
That really leaves Star-Fox and F-Zero as the missing link. Obviously, Star-Fox attempted a revival but that revival was pretty bad and the game flopped, but at the same time is there really a huge audience that wants a $60 rail shooter? $30 I would get, but for a super niche genre nowadays, full price seems like a stretch. They could go the same route as Kid Icarus and make it a hybrid between the rail shooter, and action/adventure (kind of like Star Fox Adventures) but at the same time, most Star Fox fans want a true rail shooter and not SF Adventures 2. And if they go hybrid, may as well make it a new Kid Icarus game instead, as those fans liked the direction of Uprising.
F-Zero on the other hand also struggles with the same problem, where there are fans that want a new F-Zero; but the genre itself is a hard sell for $60 (outside of party racers like Mario Kart). Most of the successful racers on other consoles try to be "ultra-realistic" in terms of graphics, and regularly get discounted (both of which Nintendo can't/won't do). So essentially both Star Fox and F-Zero are on a situation where there are fans clamoring for a second chance, but Nintendo probably thinks it isn't worth it going for such a niche audience, when there internal team could be focused on the next Mario/Zelda/whatever. Golden Sun will get a revival and KI:U could probably get remastered down the line (and maybe a sequel in like 10 years).
So in the end, Nintendo may have regressed in their usage of old/underutilized IP's (though I would argue that they never really used them in any other generation either, apart from a game here or there); but in terms of new IP's, Nintendo is doing better than ever. FE keeps on getting a little more popular, Xenoblade 2 managed to sell over 2mil and DE is around 1.5mil, Astral Chain did over a mil, and Ring Fit is at 4-5mil.