For phone calls and stuff, sure. But for identical court cases, the legal labour per-case is low. I would imagine the biggest costs are any fixed court costs like filing fees and perhaps costs of sending letters (a 60 cent stamp starts to look expensive when it's a $300 debt).
You’re missing the lower success rate of a court case. And the reputational damage to the lawyers involved. As the article mentioned, the debt collectors (by design) don’t have enough information to validate the debt is real when faced with a real challenge and not a default judgment. The article also mentions that the legal penalty of trying to falsely collect debt (which is what it looks like when they don’t have the required paperwork to fight in person) is a lot more than the actual debt. I imagine a growth in legalized debt collectors would be met with better counter-lawyers to force penalties.
