We have at least 3 currently supported vendor apps that use Python 2.7.
Too much
A lot of "data science" code in non-software companies.
Also a lot of 'unmanaged' code that was put in place and doesn't have an owner. Combined with backwards backwards compatibility (looking at you, AWS Lambda Runtimes) some of the code might not be updated any time soon because there is no value in it. This would apply to container images as well I suppose.