I often found the opposite can be be true, people can, for decades on end, be totally ignorant of what happens next door. When you show them the effect of their ignorance you often get something akin to the stages of grief. Definitely the anger, and with you in particular. The, 'I don't care whose fault it is, I'm not here to apportion blame' line only goes so far, especially since other managers and even the CEO might be very interested in apportioning blame. At least they are allies for the change that needs to happen

In terms of the expert observation, I've seen this happen a number of times in conjunction with "not invented here" (and probably been guilty of it myself at times) - "the commodity solution doesn't do X that we want", "yeah our in house solution doesn't do x,y,z that the commodity solution does but just a little more effort and it'll be perfect"

Spoiler: neither the commodity solution or the in-house solution will ever be perfect, and you should be really self critical of whether you're building something in-house to scratch your own itch.

If you can find a commodity solution with the right extension points that's often the best solution, failing that many times it's worth accepting the limitations, rarely it's worth investing in the totally bespoke thing (outside of your core domain/proposition).