If you've got a programming team, the work they deliver likely rests on the shoulders of open source giants (and Davids): the frameworks and libraries they use. Chances are that over time they received requests that the original tools could not satisfy, needed to copy them and create their own versions: the custom forks.
Once they did that, they could no longer depend on receiving improvements of the original tools by simply updating versions. They became responsible for adapting changes to their versions, or else they would be stuck on the old one, potentially missing out on important security fixes. Maybe they already gave up.
Since becoming a maintainer of a bastard version of an open source project does not deliver immediate business value, companies get stuck with stale, duct taped versions of components that are becoming liabilities. Contracting that out to a consultancy that specializes in maintaining custom forks (and maybe even getting rid of the fork by working with the original project to integrate work) could help quite a few businesses that need to write their own software.