a stranger is asking you to risk $100k on his half-baked plan in exchange for nothing, and you say "sure go ahead take my money!"? no. it doesn't work like that in the islamic world.
as a borrower who's not allowed to compensate for your lenders' risk monetarily, your access to loans is severely restricted. Essentially you have to rely on your extended family. and instead of paying for the risk with interest payments, you have to pay with loyalty and subservience.
it restricts social mobility far more than the western model. it incentivizes clan structures. which incentivize cousin marriage.
power concentrates in the patriarchs of a million little family kingdoms. which causes all kinds of economic inefficiencies.
in the US, even if you're born without any family connections, as a healthy 20 year old you can find a job (hard work) that allows you to save $70k per year and invest it. when you're 30 you have $1M and a good credit history, you can easily leverage that to get a $2M loan at low interest rates, which allows you to start any kind of productive venture you want.
and you can do all this without owing your clan's patriarch access to e.g. your most profitable clients, or your daughters hand in marriage to his retarded son, or anything else he wants in exchange for his generosity.