That's a good point, the maintenance burden of vendor libs. It may not necessarily be closed source, but for other reasons--hard math, unfamiliar language, or domain depth--might as well be a proprietary blob.

However, re-reading sph's comment above and seeing their response below, this truth table may help fill in context for me (thinking aloud and all that):

  A: Running Lisp stuff for personal
     and/or own startup
  B: Embedding the libs as a B2B solution
  C: Maintenance overhead

  A  B  C   A & B & C
  T  T  T   SkyMarshal and xwolfi's comment
  T  T  F*  I agree there would be a cost
  T  F* T   sph using for own stuff or biz
  T  F* F   Same as above
  F* T  T   N/A
  F* T  F   N/A
  F* F  T   N/A
  F* F  F   N/A

The asterisk (*) above meaning we can abort there since it wouldn't make sense to proceed to the other values.

So then B is where things went one way or the other. And admittedly, I must have assumed B.