Rewrites have a bad reputation in the business world because it's nearly impossible to sustain the political will to make it happen for long enough to actually

Rewrites have a bad reputation in the business world because it's nearly impossible to sustain the political will to make it happen for long enough to actually complete the transition, so you get partial rewrites that were supposed to be full rewrites. Open source projects are usually governed by the contributors, so there's less pressure for them to call a rewrite off early if they were all on board to begin with.