Robocalls. That said, they're likely "virtual" providers, which are in turn enabled by "Mobile Virtual Network Providers", companies that sell telco-provider-as-a-service, so that a virtual provider only needs to focus on sales, marketing, first call customer support, and legal liability but not the technical nitty gritty. I hope the FCC goes after these MVNOs enabling them next.

(source: wikipedia and I worked in a small segment of the mobile network operator market for a short while)

Many of these small voip providers the voip service is a small portion of their overall business. They may be a small ISP, reselling voip as an add on to internet services. Or they may be a small MSP marketing services to businesses in their area, and VOIP is just one small part of their overall package. If you are already marketing to the customer, providing customer service, billing, and even onsite support, why not add an additional service like VOIP, even if it alone isn't all that profitable? Even if you are only breaking even, having the service in house can save you time and money troubleshooting when a customer call you up and says they are having problems making phone calls and their third party VoIP service support is blaming the network...

Same here.

I have some questions 1) are these telcos effectively pass-thru operators for actual spammers ? in other words, just a paper entity working with 1-2 customers ?

2) Do these VOIP providers act as resellers for the big telcos ? If yes, how does the telco contracting/onboarding fail so hard at screening for bad actors as potential customers (is there a law like KYC for them at all ?)

3) Finally, once onboarded don't the big telcos have some incentive to boot bad actors from their busy networks ?

You can become one yourself this week if you install Asterisk on an obsolete PC in your closet and plug one or more phone lines into a "telephony interface card". You don't have to stay in business.

> How do they all stay in business, or get their customers?

They are created/supported by the robocallers.

By pushing new lines on you even if you don't need them, creating very low expectations for technical service, and automating away customer service at every turn.

I feel like there is a shadow cartel where all telcos agree to suck as much as possible so there's no real incentive to switch. Also aggregators love re-bills where you pay them for another provider's invoice but they can't do anything service-wise on it.

At my work (in charge of 140 Windows laptops/iPhones) the only way T-Mobile would give me a deal on 30 new iPhones was by selling me 50 new SIMs for lines I told them I absolutely didn't need. I'm turning those off now. Don't even get me started on Granite or Telepacific, each of which make Comcast and AT&T look like shining examples of greatness.

My local ISP offers VOIP.

For a long time the area was serviced by AT&T, who probably started with phone lines and then progressed over time to dial up and then more modern cable / broadband. They probably bundled in home phone service for many years.

When the local ISP built out all their gigabit fiber infrastructure they probably felt they had to offer some kind of phone service to compete, and went with VOIP since they weren't going to build out a whole telephone network infrastructure. I'd bet most people don't use it, but they need to offer it to be viable for certain older customers that don't want to give up their home phones.

I briefly set up a home phone on the provided VOIP, just for fun and nostalgia, but it was pretty annoying with sometimes getting disconnected and needing a manual power cycle to reconnect so I stopped using it.

Maybe with robocalls?