I like to think of it as a limit imposed by the bandwidth limits between compute nodes.
A volume of computers connected in a grid with cables will have a bandwidth per unit area limit along all surfaces.
Similarly you can’t “know” about other matter in some direction away from you unless the information about it traverses the network links back towards you from there. Along a line that has a fixed upper limit. With more and more matter in some direction you get less and less information about it per unit of your time elapsing. It’s like watching a higher and higher resolution video with a fixed bandwidth — it has to play slower.
PS: hence the boundary of the visible universe is also an event horizon, it is the “depth” at which the total accumulated matter sums up to the same limit.
PS: The same line of thought works for the Anthropic principle as well! In the zoo of possible universes most have zero sentient life because the rules are not conducive to it. That’s the “core concept” but there is a nuanced version where many universes have just one species of sentient life. For example infinite travel speed would allow the first aggressive xenophobic and technically capable race to wipe out everyone else in short order. Hence, we’re more likely to be living in a universe with a speed limit where such “instant Borg assimilation” is physically impossible.
