I think it's because you're thinking about it as a matter of DM pacing. The timing can be arbritrary but fictional time does matter.
It works better when the players pace the rests. That's why it's a concrete thing and not an arbritrary judgement call by the GM. In 13th Age the GM decides when a long rest happens (after roughly 4 battles) and I found it was quite disempowering to the players. The short rest also corresponds to the 'milestone' in 4E which was generally two encounters (but again DM judgement call).
And in a lot of cases it doesn't really make sense for a whole hour to pass without an incident. The DM can arbritrarily declare that there are no encounters but if they do that then that signals to the players that the DM may be willing to bend the fiction to allow them to rest.
But discussion on whether or not a location is safe enough for a short rest are tedious, as are questions like "can we take a short rest?" by which the players usually mean "nothing urgent seems to be happening right now, but we don't know if you're planning for something to happen momentarily so we need to ask". Given that it's meant to be primarily a strategic decision on the players' part as to how to manage their resources, it's easier just to adjust it fictionally so it's in their hands.
To me, an hour just isn't that long. Especially in a place like a dungeon where there's probably tons of other rooms. Let me see if I can succinctly explain why Long Rest v Short Rest really should be skewed towards Short Rest 99% of the time.
Okay, there's 24-hours in a day.
The Party wakes up at 6am to start their adventure and walks to their destination.
The party arrives at 8 am and the guardian of the destination fights them. This fight is a medium encounter.
The party decides it is too dangerous to walk into this mysterious dungeon without being discovered so they take a long rest. However, the party must wait until 10pm at night before beginning. Its currently around 8:05 am.
While waiting, the group decides to just sit outside in a secure location. The party isn't doing anything, but the warlock and monk take the time to take a short rest.
2 hours pass (10 am) and a patrol perceives the party and flees to inform the dungeon. The party can either give chase or continue their wait. They decide to stay where its safe, maybe relocating somewhere.
Patrol returns an hour later (11 am) with reinforcements but the party has changed locations. Patrol tracks them down and a finds them after 3 hours of losing and refinding the trail (2 pm).
Patrol and reinforcements together constitutes 2 more medium encounters in the day. The party decides to relocate again.
2 hours pass and the dungeon is worried the patrol and reinforcements may have been defeated so they decide to leave the dungeon with the mcguffin or whatever. All the remaining forces are moving together in case the party tries to ambush them, meanwhile, the warlock and monk has once again taken a short rest.
By this point, its 5pm. Still 5 whole hours before the party is allowed to start their long rest. The party has 2 options, continue to rest, giving the fleeing forces a head start and to possibly escape, failing to retrieve the mcguffin; or they can engage the forces and finally take the mcguffin.
If they engage, the remaining forces are worth 3 medium encounters so they must be strong. After a hard-fought battle, they emerge victorious.
As it turns out, the party had their 2 short rests and 6 medium encounters without any actual doomclock because the time naturally flows in favor for the short rest classes.
TL;DR Unless your combats are so close together that an hour can't be spared waiting until the whole adventuring encounters have occured
or you only run a single combat encounter for the day, the short rest classes will be able to find time between long rests to take a short rest.