The costs are not just for a room and food, they will cover admin, cleaning, security, exclusive use of the hotel etc.
Yes it might be dull, but you can exercise indoors also (maybe some yoga). The food might not be great but it is food. I think there's an awful lot of drama about how inhumane it is on this thread. Inconvenient, yes. Expensive, yes. Tiresome, yes. Inhumane? Have we become so soft? Let's hope there's no wars in the offing or even a more severe pandemic.
Covid isn't over, it only takes a variant that resists the vaccine who knows, one could be brewing in someone's body right now. It's easy to be nonchalant after over a year, but remember the fear and uncertainty of March 2020. The panic buying, the totality of the first lockdown, the feeling of anxiety that so many suffered. This stuff is being done for a reason.
Whether anyone agrees with these rules or not (and if Covid has taught us anything, it's that a lot of people think they are too clever or special to need to think of the greater good and follow rules), they are the rules and are a relatively known quantity .
I had to go abroad recently, didn't want to and spent the few days away stressed that I would test positive and have to quarantine abroad (possibly in a facility or hospital at my own cost). However it was a choice I took to go and no matter how pressing the reason to travel, both I and the OP did have a choice.
I wouldn't want to be in the OPs position either but I think a complaint about the food to the staff is the most constructive way forward.
Personally I would have like to have seen a South Korean style isolation with a tracking device and multiple phone calls per day to check on whereabouts, but we have what we have.