I mean:
I put them in other peoples LG and then they go into my inventory
That is what I thought you meant. However, when you worded it previously, it sounded like we can put into our own GBs and get packs from such to which can never be done.
and to be honest
why should they implement a way to put them into the invetory directly ?
Why not? With the rise of FP points with buildings, limit mechanics are outdated; even for Forge+ itself. My first thought would be putting anything in excess of the 1000 point limit as packs, but that wouldn't make sense for having Forge+; not for me, though. I would continue on getting Forge+ if they made it where (and it should be done in the first place) it can be put into packs once it it exceeds the 100 point limit (the main reason why there is a Forge+ for such). For 30 USD, this makes sense for the price. The other features of Forge+ I can do without as I do not have a problem in using the 5 diamond collect all multiple times to collect. It tied the incident collecting with it, which is good, but I collect most incidents that isn't behind a building on a road.
if they want that people keep their FP forever and collect more --> they could just remove the FP bar limit
Initially, I would be in for this. However, that would mean there will be no Forge+ for us to get; and, in turn, Inno won't make money from such. Again, if they put the previously mentioned into Forge+, then it would be worth it to spend. Just like anyone would spend to get the extras from QI or events with the passes.