This far into a season (Season 18 ends on Sunday 10th), or on non-seasonal heroes, pretty much everyone that joins public groups does so at Torment 16 on level 70 heroes. So, if your hero isn’t level 70, or isn’t capable of T16 yet, that’s why you won’t see many, or in some cases any, other players.
However, it’s incredibly easy to get to level 70 if an existing level 70 hero boosts your hero. They do this by starting a Torment 6 game (the highest difficulty a non-70 hero can join), inviting you to it, and running Nephalem Rifts together. The sub-70 gets huge amounts of XP compared to what they could do solo. Generally it takes 3-4 rifts to get someone from 1-70 in this way.
I regularly put the following into General channel in-game…
–=[ BOOSTING ]=-- Softcore. Seasonal. Send me a whisper if you’d like me to powerlevel your hero 1-70.
Or you could just ask for a boost in General chat. Someone will usually hook you up within a couple of minutes. Then, once you’re level 70, you can start building up your gear, build, and so on.
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