Termite Damage Continues As Long As There Are Termites
Live termites eat cellulose. Wood and wood products are cellulose so an active infestation of subterranean termites will eat the wood in your house as long as they are living. That is what they do.
So when a pest control company uses a termiticide like Termidol or baits or whatever means they use, it can take a while for the termiticide or pesticide to take effect. During that time, the termites are still eating your house. When that lag time from pesticide treatment to eradication is a month or so, the damage is negligible. When the lag time is years, the damage can be catastrophic.
The pest control industry likes to appease customers by eagerly treating the termite infestation but disregarding the continuous damage that is occurring. They ignore the facts that wood is being eaten and structural integrity is being threatened. It is much easier to come back and spray more chemical than try and determine how an infestation is gaining entry into the home.