Templates which generate inefficient code could be an explanation. I am reminded of an analysis* of regedit which reckoned the author(s) had probably copied a load of irrelevant code from elsewhere as a starting point.
Lotus Notes client had reasonable performance on the corporate (i.e. dated) PC I was using in 1998-2000, but I'm pretty sure it wasn't Java based at that time.
* I came across this analysis recently, but one disadvantage of working with multiple VMs is that you can't remember which browser history to search in.