Most large guilds (the ones that always manages to have a Trader in the same spot) are invite only and have a laundry list of requirements to be in it. Most others are there, they just don't actively advertise themselves and the game doesn't have a user friendly way of browsing the Guilds that are there. Everything is word of mouth.
I'm part of a small social guild, if you're a decent person, (and of "adequate age") I could shoot your gamertag over to the Guild Master.
ZOS perverted the concept of guilds in this game when they refused to implement a traditional 'auction house' and instead made it guild-based, so guilds are mainly used as a poor substitute for a real economy.Is the population very high on Xbox one?
I find it hard to find guilds but I do see lots of players everywhere!