Premiums will increase annually as insurers automatically increase the replacement cost of the building. This is done to keep up with the cost to replace the building due to inflation.
Lately, premiums have also increased as water losses have been substantial. Think of insurance as a pool where all the Condominium Corporations put in premium and those that have losses take the premium out to pay those losses.
If the losses are higher than anticipated, more premium is required to pay the losses. The additional premium is spread out amongst all, rather than just the few that had losses.