Firstly, there is a lot less security in renting. I can be evicted with a months notice. While I'm young that's part of the trade off but when I have a family I wouldn't appreciate that level of control over my life being in the hands of my landlord.
The second reason is the fact that when I fully own a house I will feel more financially secure. I won't have to worry about making rent payments for the next X years of my life and I'll feel better prepared for unforeseen circumstances. I might be able to achieve the same security by investing my money in other areas; but I much prefer investing in something tangible.
A mortgage is essentially a huge long-term bet, renting is a smaller, shorter term bet. The owner is betting that everything lines up nicely: the value of his property stays put or rises, nothing bad unexpectedly happens to the property, undesirable people don't move in around it, a whole-sector bubble doesn't pop. As a renter, there is no commitment: if the house is outdated you can move to a newer one with far less hassle; you don't have to worry about cost of maintenance; if you move during a bubble you can move once again when the bubble pops and pay less. The owner may end up with a property in 20 years if everything goes well, but a renter will never be underwater.
The second reason is the fact that when I fully own a house I will feel more financially secure. I won't have to worry about making rent payments for the next X years of my life and I'll feel better prepared for unforeseen circumstances. I might be able to achieve the same security by investing my money in other areas; but I much prefer investing in something tangible.