I love Mario games as far as I remember, but a reason I've stuck to Mario is most likely the characters, the setting, and the gameplay. I'm not 100% sure why I developed an attachment for Mario, probably because he was the first character I picked back when I was like 5 or 4 playing video games and he just became a friend. Or I played with the toy of him (the toys, which my sister brought up earlier, weren't even supposed to be "meant" for us; it was bought for my brother but we loved the toys more than he does especially when they pair so well with Beanie Babies). Could be a combination. But he was a really easy friend, and Luigi was an easy fit for my sister too, as he looks similar to Mario and he's next to him.
I avoided platformers because I was scared of dying/losing. If it was like Super Mario Odyssey I think I would've been less scared, especially with aids and stuff for younger and more timid players. Definitely didn't enjoy Mario Party until Mario Party 5 as Mario Party 5 had actual team battles and free for all just didn't jive.
I was more into Mario Kart 64 (which I hate today lol), Diddy Kong Racing, Super Smash Bros. and Mario Tennis, which I've played for ends (though Mario Tennis was rented and was a copy that didn't stick for long) but it was the toys that really got me hooked into the series. I really liked Mario Kart Double Dash and Super Smash Bros. Melee going into the GCN years. I eventually eased myself playing single player games including Super Mario 64 DS (I think that one was the first step into the unfamiliar single player Mario game), New Super Mario Bros. DS, and Super Mario Galaxy (I still remember in Galaxy being not 100% comfortable with all challenges).
Going on today, I'm still more of a stickler for Mario spinoffs and I tend to look forward to new Mario Sports barring the Olympics (as disappointing they seem to be getting every new installment) and Mario Party the most, but a lot of my Mario needs are usually fulfilled by weirdly nonMario games including Super Smash Bros. and modded games including Rivals of Aether, Garry's Mod, Left 4 Dead 2, Spore, and The Sims (but I also get fulfillment with a bit of roleplay and just talking about Mario). I'm not sure when was the last "true" Mario game I played, except I did play some Mario games over on emulator including Power Tennis, Super Mario Sunshine, and Double Dash. But as of recent, I don't have access to many Mario games legally as I have only a Switch and a really good desktop with an Intel Xeon W-2295 and a GeForce RTX 2080 SUPER, and that just seems to be a perfect setup for emulation. I've also skipped on a fair few recent Mario titles including Mario Tennis Aces, both Super Mario Makers, Super Mario 3D World + Bowser's Fury, and I'm not wholly enthusiastic about Mario Golf Super Rush; and I didn't complete Luigi's Mansion 3 or Mario + Rabbids Kingdom Battle and didn't even start Origami King before I moved out.
I hoard Mario plushies, so I don't think my fondness for Mario is really going away even if I'm not playing the video games as religiously as I used to. I still certainly interact with the Mario content like a Mario acolyte, just not through the Mario video games.
I haven't played much of the literal classics. Most of my exposure to the older games were from the Advance series and I believe just the voice acting alone makes it a better experience than the classics. That being said, Super Mario Advance (Super Mario Bros. 2) I enjoyed the most out of the series and as for the older games, and even factoring the fan favorite Super Mario World and Super Mario Bros. 3, I didn't enjoy them as much as New Super Mario Bros. or New Super Mario Bros. Wii or Super Mario 3D World or Super Mario 3D Land BUT they're still solid games.
I know the topic is supposed to center on the platformers, but I feel leaving out kart, party, sports, smash bros., merchandise in the discussion leaves a HUGE gap about my time spent with the Mario series; it's the reason I started and stuck with the Mario series in the first place. As I said, I wouldn't have played the platformers and probably would be less likely to play Mario, much less love the guy, if my opportunities were stuck to just playing Super Mario World in SNES rather than playing as Mario in Smash Bros., driving as Mario in Mario Kart 64, playing as Mario in Mario Party, and developing an emotional attachment to a Mario doll.