Not necessarily. My understanding is that worms do not like salty environments, but I could be wrong. If so then if your soil is salty from being coastal or possibly salty from continued use of salty fertilizers or snail killers, that might affect the earthworms. Do you use organic fertilizer? Using organic fertilizers should help.

I have dug into my yard in Bandera many times and never saw earthworms; however, recently, after 20 inches of rain in a few weeks, I do see the occasional worm on the driveway.

Does MicroLife products count as organic? If so, I've been using them all this year.

What you call "hard clay" is probably heavy silt. But in either case, the earthworm considers that a minor challenge and nothing more.

Saltier soils, as David mentioned, will deter earthworms. And less organic soils will also reduce their numbers as they have little to eat.

MicroLife fertilizers look to be hybrid fertilizers; there's no easy way to get potassium levels that high without adding potassium sulfate (a salt) or worse, potassium chloride (a strong salt). Both are allowable in an organic regime, and in neither case is it all that much.

With adequate rainfall or irrigation, it's not a problem, however, except in that it's a slight stress on the lawn. And of course the one they label as "hybrid" actually does use a synthetic nitrogen source (another salt) as well as a potassium salt.

A year isn't a very long time with those, however. Over two to four years you should notice an increase in worm populations from near-zero to very high.