Garmin has so many different trackers for different niches. Scuba, hikers, bikers, runners, pilots...
I switched after getting my third Fitbit replacement under warranty. Affordable and standard watch band parts, though some high-end trackers are a bit pricey for me.
Just no reason to stay with Fitbit with Google's history of product longevity and support.
I owned four Fitbit devices, and they all broke in some way. The clip broke at the middle joint. Everything else always was at the wristband to body joint, and they refused to make standard wristbands. I've had a Vivoactive 3 since 2018-ish, and it still works for me, plus I can have custom activities, and watch faces, and data screens. I like that my partner's Garmin and mine use the same charging cable, too.
Disclaimer: I don't use the smart watch features, like texts or calls or notifications of any kind on my tracker, and the battery lasts about five days still, unless I use GPS.
I finally replaced my pebble with a Garmin. Pleasantly surprised. I still miss voice response and proper tasker integration, but otherwise it's a solid smart watch.
Activities I only use for hiking. I don't wear a watch cycling or kayaking. Looking forward to trying the snowboarding activity though.