Putting a theory of "you shouldn't trust pilots" into ATC breaks the entire system.
It is a system built out of very regulated parts, very professional people, and tight controls.
Pilots are encouraged to be very forward and proactive about fuel situations because of https://en.wikipedia.org/wiki/Avianca_Flight_052
Minimum fuel requirements are calculated as "Time of fuel for cruise to certain points", which is usually good enough, but if an Airport is stupid busy, or has bad wind patterns, just a couple go-arounds will chew through your fuel way faster than the regulation expects.
Turbofan engines are also dramatically less efficient at low altitude than high altitude cruise. So holding at low altitudes because a congested airport is dealing with traffic will chew through your reserves much faster than you expect.
Ryanair flies short hops to congested airports. They will have relatively low reserves, and you should expect them to run into "Hey we are low on fuel" more often than international flights for example.
> It is a system built out of very regulated parts, very professional people, and tight controls.
also worth mentioning that most of the civil aviation regulations and SOPs regarding commercial flights are written in blood.
"It is a system built out of very regulated parts, very professional people, and tight controls."
Locally, this is true. Globally, not so much. I remember my friend's vivid description of a flight taken in Nepal. It was absolutely wild.
I mean, obviously, it's better to trust the pilots, but if they are jumping the line because "fuel low" when it's not low, well, they're not being very professional, are they?