That's how it works where I work (hospital). 90+% of the time, my job function is no different from what I'd be doing telecommuting. Not only that, we have a moratorium on moves/adds/changes on Mondays and Fridays. If I'm not visible while creating heat+CO2, it isn't considered "working".
2 years ago because of the "bad economy" they took away 6 days of PTO. Because we're healthcare, and our management is nearly braindead (maybe just lazy) when it comes to certain things. All employees are treated the same whether clerical or clinical. We have NO normal vacation days (Xmas, Thanksgiving, 4th of July, etc). Used to be you could elect to work on a holiday or not. I used to work a lot of holidays and save the vacation for when I had custody time with my kids. Shortly after they took away the 6 days of PTO, they made 6 holidays mandatory. SO, in the space of less than a year, I'd lost as much as 12 days of vacation time.
We do have a long-term sick bank, but you have to burn 40hrs of PTO before the LTS kicks in. If you don't have 40hrs? No pay for the interim. I have trouble keeping 40 hrs as it is, and almost 700 in LTS.
I had already given up a week when I went to work there (more, since holidays didn't count against me in the prior job). I now have to be very jealous of my days off. Add even newer rules about being "tardy" (how can someone who is salaried and works over 40 hrs/wk and is on call all the time be tardy???). Other rules that get you a write up if you call in sick - you're supposed to go to work and have your manager send you home(?!?!). The list goes on.
I thank the jerkoffs in Washington under Bush's cronyism rule for taking the teeth out of the FLSA. The rule changes here went into effect as the FLSA rules went out. My wife's employer is even worse. Shit that would never have gone on 5-6 yrs ago when salaried IT workers had at least a little protection against being indentured servants. There's a reason corporate profits are at an all-time high. As soon as my kids graduate HS, I'll finally be free to get out of this shithole in the Bible Belt and move somewhere with at least a little sanity and job competition.
TL;DR: Employers take advantage. Employees don't like getting ass-raped for being sick, so they come to work sick.