How fast does periodontitis progress?

[Dave001]

I have been recently referred to a periodontist as I have deep pockets and bone loss on at least one tooth. I have brushed twice a day, floss daily and get dental cleanings twice a year. I even recently had two root canals. Yet, all these trips to the dentist and now I have serious dental problems? I'm feeling like my dentist and his hygienists dropped the ball. Should they have caught it and treated it earlier? How fast can periodontitis progress? I thought I was doing what I needed to for oral health and now...Any input is greatly appreciated.