NewEnglandfag here. No change in frequency for at least the last three years by my observation. Not daily, but nearly so.
There are a few theories for chemtrails being done for positive reasons.
One is the UV shielding. There's a theory by Clif High (and possibly others) that the Sun is putting out far more high-energy UV (above UVB/A). This is damaging for all living things on the surface.
Another is that we are entering a phase of global COOLING, and this is an attempt to create a greenhouse effect to keep the Earth warm.
Could be both, could be neither.
One thing is for sure, it's happening. I'm an oldfag and the sky never looked like this until about 10-15 years ago (never looked like this 20-30 years ago).