How'd she manage to get well-fitting suits back then but is unable to now? It's not like she can't afford to have them tailored or customized.
my guess is as a dainty woman back then she was trying to look good and fashionable, now that she is a man she just buys them off the rack. and being such a manlet they dont tend to make them small enough for her.
It's because, in part, she's not dressing herself.
The tragic tuxedo is from the Met Gala. The way the Met Gala works is unless you're a top notch a lister that Anna Wintour deems fashionable, you do not get a direct invite. Designers selected by Anna Wintour buy tables at the Met Gala (this is how it's a gala- that's how they raise the money) and then invite celebrities who weren't otherwise invited to model their clothes.
The idea, of course, is that people like to look at celebrities and find out what they're wearing, so if you get some cool celebrities to sit on your table then the magazines and gossip websites will share lots of photos of your designs. This was Ellen's first red carpet as Elliot so she was going to get focused on (I note she's not been invited back since).
In Ellen's case she got invited by Balenciaga and that year Balenciaga had launched a variety of comically oversized suits:



For whatever reason the designer deliberately designed suits that didn't fit the way a suit is supposed to (sleeves too long, shoulders too big etc).
The guests then get dressed by the fashion house. How much leeway a guest gets really depends on how much the designer wants them there and how famous the guest is. I'm pretty sure they just showed her a rack of giant suits and told her which one she'd be wearing. Even if she wanted to swap it out for something else, there likely weren't any suits on offer that did fit, and she couldn't ask Balenciaga to tailor the suit to fit because that defeats the point of getting her to show off their oversized suits. So she probably just got watery eyes and put the tux on. They added in a green corsage as a reference to a green carnation (an old gay man symbol).
The next time she appeared on a red carpet was the Balenciaga fashion show. This was a weird one because they made their red carpet into the fashion runway as well and had models walking it - and Ellen was actually there as a model (again, to get clicks). Models have even less say in what they wear and so -

Again with the oversized suits and the amusing clown shoes. Honestly it does kinda feel like Demna Gvasalia wanted to humiliate her lol.
Since then she's been a brand ambassador for Gucci. Celebrities who are brand ambassadors get paid a bunch of money to wear specific pieces on red carpets or out and about to increase the visibility of those clothes (it's become a meme that Chanel can't dress actresses so any actress who's a Chanel ambassador ends up looking frumpy for a couple years). By accepting the contract she then has to wear some Gucci stuff. You can see it actually fits, but Gucci has its own design ethos which isn't flattering to Ellen either

That said while most of these outfits are Gucci, these shirts aren't-

- they're Todd Snyder, so she gets some lee way. Todd Snyder isn't terribly well known but is revered in fashion circles, and "putting brown and black together" is apparently a cutting edge trend, so that tipped me off she's got an interesting stylist. Sure enough

She hired Pete Davidson's stylist. That does explain a lot.