If you have a pre-existing relationship with them, sure. If they're your friend, boss, your mum, your teacher, your neighbour, then it's normal (in some cases required) for them to have an interest in your circumstances and care for you and the reasoning behind your rude behaviour, even on a superficial level. ("Sorry, Neighbour Bob, about not trimming those tree branches like I said I would. Work has been killing me lately and I worked a double shift on Saturday and then I was visiting my grandma in the hospital on Sunday. But I'll try to get to the pruning this weekend." "Oh hey, no worries, Neighbour Coalie, hope your grandma is doing better!)
But we're talking about two relative strangers in a fic exchange, with the only level of interaction between them being one of them was assigned to write a story for the other, and that person then failed the basic exchange etiquette of writing them a comment. It's rude, but it's like someone bumping into you on the street because they weren't watching where they were going. Maybe they do have a good reason. Or maybe they're just an asshole. The person being bumped into has no reason to care and shouldn't be required to care; they're the one who was 'harmed' (of course recognising that it's a fic exchange and any harm here is extremely minor). But you've already put stuff onto them by not holding up your part of the exchange, and then you want to put more stuff onto them by expecting them to listen to your explanation and care about your circumstances.
And it IS different than just simply apologising to them. "I'm sorry I didn't comment in a reasonable amount of time." That's how you acknowledge it was a failure on your part. Saying 'sorry' and writing a late comment is how you amend for the failure. Adding "but I was suffering from mental health issues and the following bad things were happening in my life and I was in hospital and my dog died and I let fandom things fall by the wayside because personal issues" is not about making up for the etiquette breach. It's about you feeling bad about your etiquette breach and wanting your writer to tell you that it's okay, that your circumstances are understandable and acceptable, and so the etiquette breach didn't really matter at all. Which is probably true, all things considered! Shitty personal life stuff should take precedence over fandom stuff! Someone who fails to comment on an exchange fic and then comes back a few months later when they can shouldn't feel especially guilty about it. But also, they shouldn't try and make it their writer's job to tell them that. Because it's NOT their writer's job to tell them that. So just say hey, sorry it's late, but here's a nice comment on the story you wrote for me. And manage your own feelings about your failure yourself.
Re: Stupid Questions
But we're talking about two relative strangers in a fic exchange, with the only level of interaction between them being one of them was assigned to write a story for the other, and that person then failed the basic exchange etiquette of writing them a comment. It's rude, but it's like someone bumping into you on the street because they weren't watching where they were going. Maybe they do have a good reason. Or maybe they're just an asshole. The person being bumped into has no reason to care and shouldn't be required to care; they're the one who was 'harmed' (of course recognising that it's a fic exchange and any harm here is extremely minor). But you've already put stuff onto them by not holding up your part of the exchange, and then you want to put more stuff onto them by expecting them to listen to your explanation and care about your circumstances.
And it IS different than just simply apologising to them. "I'm sorry I didn't comment in a reasonable amount of time." That's how you acknowledge it was a failure on your part. Saying 'sorry' and writing a late comment is how you amend for the failure. Adding "but I was suffering from mental health issues and the following bad things were happening in my life and I was in hospital and my dog died and I let fandom things fall by the wayside because personal issues" is not about making up for the etiquette breach. It's about you feeling bad about your etiquette breach and wanting your writer to tell you that it's okay, that your circumstances are understandable and acceptable, and so the etiquette breach didn't really matter at all. Which is probably true, all things considered! Shitty personal life stuff should take precedence over fandom stuff! Someone who fails to comment on an exchange fic and then comes back a few months later when they can shouldn't feel especially guilty about it. But also, they shouldn't try and make it their writer's job to tell them that. Because it's NOT their writer's job to tell them that. So just say hey, sorry it's late, but here's a nice comment on the story you wrote for me. And manage your own feelings about your failure yourself.