I would imagine mature organisations without serious short/medium term existential risk due to product features may build some push back mechanisms to defend against the inherent cost of maintaining existing business (ie prioritising tech debt to avoid outages etc).

In general, it is a probably a mix of the two - even if there is a mandate from up high, things are typically arranged so that it can only occupy X% of a team’s capacity in normal operation etc, with at least some amount “protected” for things the team thinks are important. Of course, this is not the case everywhere and a specific demand might require “all hands on deck”, but to me that seems like a short-sighted decision without an extremely good reason.