Thank you roar reaching out.

It really really likes its spot!  You seemed to haves trimmed it correctly.  You have a paniculata hydrangea-I’m not sure which variety, but they bloom on new wood.  They can be cut back to 2 feet if you want to.

 Different shrubs are meant to be a distinctive height depending on the variety and you can’t stop them from growing that size.  The heads just get too heavy.  You could try propping up the stems, but that will take away the look.  Unfortunately it is what hydrangeas do.  Because of the time they bloom you don’t want to trim them mid season and that would be the only way to stop them-keep trimming- but you’d get no flowers.  
Depending on how old they are, you could try to move them and put in a shorter variety. I personally think they’re beautiful.

I wish I could be more help, but you can’t stop them from growing and flopping.

Maybe another thing to try is to gently shake off the water when it rains hard.

Good luck and happy spring!