The initial obscurity of the cello suites was part of the larger disregarding of Bach's work, in the shift from baroque to classical style. But did the "re-"regarding of the cello suites happen at the same time as Mendelssohn? Or did Mendelssohn only start the process, by rediscovering a few good pieces, while other pieces like the cello suites waited another ~hundred years?
My understanding is that both Mozart and Schubert started to fall out of fashion in the early to mid 1900s for being "lightweight" and just stepping stones to Beethoven. It took some dedicated musicologists from Britain who championed them in the 50s to really solidify their standing in music history.
I also believe we are now seeing a resurgence of interest in Salieri in part thanks to the movie...
The cello wasn't a popular solo instrument. Pablo Casals was a celebrity who made the instrument a much bigger deal. The cello suites rode on his celebrity.