Player limits are there to encourage people to use multiple blocks (otherwise tons of people would probably just flood into a single block), and blocks exist to keep strain lower on the server. As you put more players into a single space in any kinda networked game, server strain (data usage, cpu, etc) is going to increase exponentially, and you can mitigate that by separating the population into multiple groups. That basically applies to anything where a player interacts with everyone else in a zone, whether it's sending a chat message or a player running around and that movement being shown on everyone's screens, etc. You can see the same kinda thing in other online games too, like when a new expansion comes out FF14 will sometimes throw up multiple instances (blocks) of cities (like lobbies) with player limits for the same reason (alongside outdoor zones too, but that's besides the point here) as the population erupts.
I can definitely see how it would feel bad for a free player though, and it would be fairer if there wasn't a Premium overflow that could basically lock free players out of a chance of entering a block, but at the end of the day it's a F2P game and they've gotta entice people to spend money on it. Maybe you can get into an alliance or a group chat that does a decent amount of triggers?
It's probably worth mentioning that in what we've seen of NGS, they've confirmed that there'll still be player limits on all outdoor zones like in PSO2 (despite being open world), so I would expect that the block system would stick around in the lobby city/cities in NGS too.