Some roses do this, so it might just be the particular variety you've got, but sometimes its poor pruning technique - when pruning is done (usually late February/early March, if they're not ramblers) its usual to cut off anything that's thin and weak, so if you're not doing that and those stems flower, they're not strong enough to support the flowers. As I said, depends on the rose variety - which you've not specified.

What varieties do you have? Ramblers and climbers will need something to climb up and you can provide additional support to stems by loosely tying them to the support.
If you don't want to use canes, you could try proper plant support rings, but they would be better put in place early in the year so that stems can be fed through as they grow.

I think it's the particular cultivar. As stated above, not much you can do. The genome of the plant is coded to do this- inferior stems.

Thank you. I have only one with a name, it's called (Teasing Georgia)
I'll have to look up on pruning, it could be that.

Thanks again. Gail