I've been trying to work out why it bothers me so much as well. I think its a combination of things but mainly its the duplicitous nature of selling this way. The bloggers should just be proud of the fact that their IG following has opened up these work opportunities, their followers will be happy for them because they are loyal and already like them.
I follow plenty of brands (and often ones featured on bloggers pages) but the relationship with them is more upfront - I know where I stand with it. I really don't mind when bloggers say "X approached me to work with them on this project". You know that its a work/marketing activity and the pictures are related to that work. They show every other aspect of their life so why would it be any different to show their work in a work context rather than pretend its just day #dayoutwithhubby. Why not say, "Chewton Glen invited me to a cookery day so I could show you what its like there and how fantastic the cookery workshops are"? FINE. (would feel awful now if it actually was a Christmas present from hubby, but that's the point - its not clear).
Reading IG it's easy to sometimes think its just you that doesn't like it but when the ad posts are interspersed with regular posts you can see the likes go down by hundreds (thousands on the big accounts) so it does look pretty obvious that people in general are turned off by ads in the IG content.
I admire more the bloggers that do other things with the platform that IG has given them - the ones that go on to do interiors workshops, set up their own online shops, do styling workshops, even write books (as long as they wrote it themselves), rather than the ones that flog stuff on their page without telling you that's what they are doing. I also think it's the latter type that are being taken for a ride by the brands (the bigger brands anyway)