One one side, you have the analysis libraries, who inherited the knowledge contained in the older FORTRAN libraries. From this point of view, both ROOT and its predecessor PAW, are excatly what you could expect from CERN: highest quality, thoroughly debugged and everything you may need as a particle physicist.
On the other side, you have the programming framework... and that's a different matter!
When I worked in the ATLAS data acquisition group, ROOT was frowned upon! Libraries were ok, but we needed a sane environment and we built it.
ROOT as a framework gave me the feeling it had been designed by inexperienced self-taught-from-trade-magazines developers who thought learning a bit of programming was too much hassle for the average physicist and thus they had to dumb ROOT down a lot.
But, as Mr. T reportedly said: it takes a smart guy to play dumb!
I’m not sure exactly how dependent particle physics is on ROOT, so direct comparison is difficult.
FWIW in my department (Electrical Engineering) No one is using SNOPT for their work that I know of.