Because in my experience, and that of almost everyone I know, you get warnings, arse kickings, and nasty, snide little letters from the manager threatening to issue a disciplinary if you DARE to be ill and have a day or two off.
DH had 2 days off sick in July 2024, and then 2 days off sick in June 2025. First days off sick since Summer 2021. (And then it was only 1 day that year!) Last sick day before that was 2018. When he got back, (in June 2025,) there was a spiteful, shitty, and threatening letter from his manager warning him that should he have any more time off sick he will be very likely to receive a disciplinary, which could of course, (if he has further time off) result in dismissal. Him having 4 days off (2 periods of sick time) in the same 12 month period, had 'triggered' a first written warning. 🙄
The last thing he needs in his late 50s. Who the fuck is going to employ him, with very few qualifications, and at nearly 60, and give him the same 30 hours a week guaranteed contract?! (He has been there for 17 years, and is one of the last to get a 'decent amount of hours guaranteed' employment contract.)
When my (bemused and puzzled) DH asked 'well I can't very well never have another day off sick, I don't know if I'm going to be ill, how long is this 'warning' for?' he got told 'a year.' So if he is off sick for a single fucking second before mid June 2026, he will be pulled up and receive a disciplinary. Fucking joke. You can't help being ill. So yeah, he said even if he has covid, or flu, a sickness bug, dysentery, ebola, or diptheria, he is going in! 'Be careful what you wish for' he said (about his employer.)
But yeah tr;dr @slippedawaylikeabottleofwine THIS is why some people go in when they're sick!!!!!
Oh, and yes, as many people have said, some people don't get paid when they're off, so they can't afford to be off!