There are a couple of reasons for that. One is affordability. People can't afford to buy homes, whether they're ground-oriented or in a high rise, so they're moving towards rental.
The other thing is that the rental market has been helped quite a bit by changes in taxation policy and other financing that has been necessary to better equip industry to make projects pencil out. For the longest time they weren't. Therefore, industry was building condos and selling those units into the secondary market.
The changes that have been made to make purpose-built rental more viable have been important and good to help that out, but again, we can't be trading off purpose-built rental and building a lot more of that and fewer units for ownership. We need more units for ownership as well.