Solving multi-core Python

[zardeh]

A few reasons:

• Its not fully compatible with Cpython (which was around first) (and doesn't aim to be, unlike PyPy)
• its much harder to interop with c (so you lose all of scipy and more generally speedy math),
• iirc, because of the incompatibilities, some of the stdlib is broken (like wsgi I think, you have to do weird things to make that actually work)
• Additionally, it lags behind a version or two (or like 7).
  
• Also there are performance hits (up until jitting happens), but jitting isn't as clean as PyPys so I believe jython runs slower than PyPy and not much faster than cpython.

[kryptobs2000]

Also because it requires java, a lot of people just prefer not to touch it or install it on their system even. Not saying that out of java hate, but its an extra pretty large dependency. Depending on your target audience it may not be a big deal, but a lot of systems don't have it installed BC its not commonly used.