Your service must work so well it became invisible and forgotten. That's quite the feat. Congratulations.
However, that said, I think in the majority of the actual cases I'm describing above the cause is more a combination of 1.) the surprising percentage of tech companies that appear to be in a state of continual organizational dysfunction and 2.) how API's are inherently a background type of thing like lloydatkinson wrote!
In about 1 in 10 cases I'd also say the cause is actually because of merger/acquisition - which is just always a complex and organizationally challenging process.