You will notice that most “investors” will not mind locking in their funds for longer period of time. Yes, of course, as fund manager you need a solid contract then. Many will even pay a fee for managing their funds too.
Yes, times are changing and this is an unregulated stock market mostly.
There definitely is a model achievable. Whether it is a healthy one or a card house, that’s a different debate.
“They’d have to take a chance” is as much a protection as an inconvenience to them.
If you offer a high ROI there’s probably going to be inconveniences in the model as well. Most know that.