The scarce thing is contact and confirmation, and that hasn't gotten cheaper. A list tells you a notice was filed. It doesn't tell you the house has been vacant for eight months, that the roof is open at the back corner, that the occupant is a tenant rather than the owner, or that the number on file rings a disconnected line while the heir lives four states away and answers a different one. Every one of those changes whether the address is worth an investor's hour, and every one requires someone to physically look or actually reach a human.
What has changed is the shape of the fee. When lists were the product, a bird dog got paid for the address. Now the address is table stakes and the fee tracks how much verification you attach. A raw address off a list pulled the same day by fifty other people is worth close to nothing. The same address with dated photos, occupancy confirmed, and a number that a person answered is worth what it always was.
One counterweight to your growing-supply point: rising filing volume raises the count of addresses, and it also raises the number of people working them. A pre-foreclosure list in a mid-size county gets mailed by a dozen operators inside a week. Being early stops meaning early on the list and starts meaning early relative to the filing, which usually means noticing the house before the paperwork exists. Code enforcement notices, utility shutoffs, and a lawn that's changed in six weeks all show up ahead of a public filing.
The risk in a verification-first model is that it doesn't scale. Thirty verified addresses a month is roughly the ceiling for one person on foot, so the income has a hard cap, which is why most people treat this as a stepping stone rather than a business.