I don't think they'd have an aversion to buying a piece of legacy software written in Lisp if said software had a proven revenue stream and was part of the core

I don't think they'd have an aversion to buying a piece of legacy software written in Lisp if said software had a proven revenue stream and was part of the core underpinning to a major category of search they want to get into more. However, it's reasonable for them to be averse to writing totally new projects in Lisp, in-house, because when you're at a huge company as a general rule you don't want dozens of different languages in use: it's inefficient and you lose out on a lot of opportunities to leverage skills across teams and across service layers if you do that. Lisp, from what I heard, didn't make the cut, despite it's strengths. They still allow a few though, and I believe they are Python, JavaScript, Java and C/C++.