Why does the point-to-multipoint OSPF network type generate the /32 routes and how can I stop them from being advertised?
The behavior of point-to-multipoint is to advertise each end-point out as a /32 and suppress the advertisement of the network itself. Point-to-multipoint advertises the end points to overcome possible reachability issues between devices that are on the same logical subnet but do not have direct communication (i.e. spoke to spoke communication in a hub and spoke environment). The OSPF point-to-multipoint and loopback network types do not advertise the network itself but advertise a host route for each end-point. This is as per the RFC.
If you want to suppress the /32s and advertise only the network, you would need to use an OSPF network type other than point-to-multipoint or configure the network to be in its own OSPF area. After the network is put in its own OSPF area, use the area range command to summarize the /32s so other routers only see the summarized route.