"There were no major breakthroughs done by Hubble. "

Oh, I don't know about that, Raoul. There are now images of what are believed to be the planet-forming dust clouds around other stars, helping to concretize some of the theories in that regard, as one example. I think overall it's been a plus, though I do think that the data returned has been under-studied, and perhaps having a break from the Hubble will allow some time to reflect on the data we did get.

"It's because the teams who were allowed to use the HST had to present their project years in advance and it was peer reviewed and any out-of-the-ordinary project was going to be suspect."

I think the severe constraints on time were a factor also. Projects that didn't address the grand themes promulgated by the science committees, NSF, CNRS, etc., were given less priority than those that did. Just imagine if amateurs were able to get time on the Hubble on the internet...

"The thing the HST had like no other scientific project, was a huge PR, lots of money to share pictures with as many as possible, access to media not normally linked to science."

Oh yeah. Those small prints they handed out like candy were golden. I had to give up one to a little girl on the tram in Strasbourg. I was reviewing my class notes (Hubble that day) and I could see her eyes fixed on this one image. I showed it to her, expliqué ce que c'était (aussi bien que je pusse), and knew that I wasn't going to get it back (at least not without being the mean American). Oh well.

As fond as I am of the Hubble, though, I do recognize that it's time to let it go and move on to the next things.