I'm not sure whether it's by design or instructions or what but usually by the time we get in and around the box (which Pogba is often involved prior to) Paul is hanging well back with his hands on his hips. I say this as someone who has often owned him in FPL and shouting at him to get into the box!
In contrast, Frank was the master of the "late run into the box" - it was his trademark and best asset
Problem is we play too narrow, and beside Lukaku the other attackers also want to join the attack. We just don't have the creator. Even if we overload the box, the chance a good cross would being put in is slim. And Pogba is not the type who come as the first wave of attack either. Since he is a more potential attack builder and creator, he is used to get more involved in the other phase than trying to run into the box waiting for someone to create.
Lampard is different, and as Mourinho put it Lampard is less ideal than Sneijder and Deco. If you look at goal scoring stats, then you would have thought Deco and Snejder was underwhelming in their best season playing more as 10 by Lampard standard. Remember Pogba was not supposed to be the no 10 to begin with.
All in all, Pogba is not really supposed to be a Lampard at least until we solve all our creativity problem (Alexis helps a little and hopefully he would gel in next season and boost the team creative performance consistently). Pogba can do much even if he's not supposed to to be a Lampard as his potential show, that's what Lampard is right, and Mourinho wants to provoke Pogba to squeeze that out, that's a common knowledge shared & confirmed not just by Lampard.