Manufacturing is a large industry, but it's what China was targeting in the 1950s. They're aiming higher now. Most of the tech transfer is around next gen industries, such as batteries.
And as for who is forcing foreign companies to do this? Hilariously enough, capitalism. Multinationals can't afford to miss selling to the Chinese market, or their board / shareholder's vote them out. So they're left to strike the best deal they can get, given that the outcome is already known by both parties. (Exceptions like Google exist, but it does have an atypical stock structure)
From the Minneapolis Fed (2016), https://www.minneapolisfed.org/research/economic-policy-pape... (the first authoritative source I could find):
"China’s quid pro quo policy also helps account for the unusual global investment flow. Chinese policy requires multinational firms that want access to China’s huge market to transfer partial property rights to their technology, often through R&D centers or joint ventures with Chinese firms (Holmes, McGrattan and Prescott 2015a, 2015b)."