Nintendo has typically been good about getting developers to support their handheld hardware, unlike the more spotty track record of their consoles. That being said, looking back in hindsight, the Nintendo 3DS was an anomaly in that for a Nintendo handheld, it was oddly lackluster in third party support, especially compared to the likes of the DS or GBA. 

First, western support took the biggest hit. Back in the DS days, you had everyone from EA, Ubisoft, even Rockstar releasing interesting stuff for the DS. Hell, the DS got versions of every CoD game since Modern Warfare. But with the 3DS, western developers dropped support for it as quickly as they took it up, and they never really picked it back up again either. Japanese developers fared a bit better, with Square Enix and Atlus heavily backing the system. But even that was a bit of a step back from the DS, as many of the more unique games the DS was known for were almost non-existent on the 3DS.

Even indie support was underwhelming. Due to the 3DS' lack of engine support and clunky hardware, many indie games skipped the platform altogether. So, yeah, the 3DS' 3rd party support was disappointing. I love the 3DS, it's up there with Nintendo's best on the first party side. But it's much more of a Nintendo box than some fans like to admit. At best, it's on par with the GameCube and Wii (that is okay, not great, not terrible), and at worst it's a massive step back from its predecessors. The Switch however looks to bring things back to DS and GBA levels of support, especially if more stuff like Octopath an Ninjala keep coming. 

I'll wait for Rol before I have an opinion on this.

edit: What Rol said.

The 3DS is probably my least played platform that I have owned over the last 30+ years... I think the subpar displays and visuals play a big part of that. (I am a resolution snob.)
I mostly grabbed it for the Nintendo 64 ports. Aka. Nostalgia. Ocarina of time, Lylat wars etc' are amazing.

Likely because devs/publishers who had smaller budgets and wanted to put out small titles could do it on consoles as digital titles.
So when a Ubisoft or EA wants to put out a title that would previously have been a handheld game now instead make a Child of Light or Unravel for consoles.

Compared to GBA and DS, 3DS was severely lacking in 3rd party support. I think what happened is those resources were moved to mobile devices like phones and tablets.

I have no regrets buying a 3DS, but I didn't play any JRPGs and I probably completed like 10 games at most. I spent more time with the Vita.

Yeah it became the system for Nintenod's own franchises and visual novels. But at least Nintendo's own efforts were great

It's a good console but yeah lacked support. Like said before, they migrated to mobile devices and that hit the system hard. If it weren't for Nintendo's great support it would've flopped

It had it the place where it was needed, in terms of RPGs :)

Look at what Atlus did for the 3DS:
Shin Megami Tensei: Devil Survivor Overclocked
Shin Megami Tensei: Devil Survivor 2: Record Breaker
Shin Megami Tensei IV
Shin Megami Tensei IV: Apocalypse
Shin Megami Tensei: Strange Journey Redux
Shin Megami Tensei: Devil Summoner: Soul Hackers
Persona Q: Shadow of the Labyrinth
Persona Q2: New Cinema Labyrinth

Etrian Odyssey Untold: The Millennium Girl (remake)
Etrian Odyssey II: Untold: The Fafnir Knight (remake)
Etrian Odyssey IV: Legends of the Titan
Etrian Odyssey V: Beyond the Myth

Etrian Mystery Dungeon I
Etrian Mystery Dungeon II

Plenty of 3rd party put in effort to help the 3DS.

Well I think we can call it the Japanese 3D bet display disaster. Back in 2010 almost all keita manufacturers and even Nintendo thought 3D is the next big thing. And then an American company named like a fruit conquered the market with apps and touchscreens.

I think the PS Vita was even a much stronger western approach to handheld gaming and even Sony didn't reached western game companies at that point. Given the time and the smartphone boom, many devs just didn't believed handhelds will still be a thing in the future and concentrated themselves on their core markets or started mobile gaming business sections, like EA, Ubisoft, 2k Games, Activision Blizzard, Bethesda and most recently even Nintendo did.

Tbf, Atlus have 6 SMT games, 7 Etrian Odyssey games, Radiant Historia remake. Not to mention, the first time we have Persona game on Nin system with PQ1 & 2 though just spin off but still canon to the story, that is way more than DS, not really a step back. Level 5 support for it also is way better than DS. In 8 gen, Western support focus on smartphones, 3ds and vita only have some Western games at several first years and then, Japan games only for both and some indie games from the West. Named Octopath, you shouldn't ignore Bravely Default/Bravely Second. I agree that 3ds have 3rd party support worse than GBA/DS but not all are step back, it is a JRPG heaven