https://startyourownisp.com/posts/fiber-provider/
If you just Google then it's usually called leased or dedicated internet
Just some (US) examples
https://www.business.att.com/products/att-dedicated-internet...
https://business.comcast.com/learn/internet/dedicated-intern...
https://www.verizon.com/business/products/internet/internet-...
Or if (technically/financially/legally) possible, even run your own fibre to a PoP housing an IXP on your own.
Once you're in multiple PoPs and on multiple IXPs and with multiple upstreams/peers you're pretty much independent from the whims of a single ISP.
But also because once you're in a single location, you can pretty easily get multiple providers to that location for a Price, so there's really no point. Even small rural towns usually have multiple internet connections from different companies, and if they don't you can pay to run fiber if you really wanted to.
People find it hard to believe, but Comcast et al are actually businesses, not Satan's marketing department; and they happily take money even from "competitors".
I'm not an expert but afaik you can't just be a Tier 1 network member https://en.wikipedia.org/wiki/Tier_1_network
Even Tier 2 very limited https://en.wikipedia.org/wiki/Tier_2_network
In this guide's case yes you will be akin to an MVNO, you won't peer but just buying transit traffic. That's why most of these guides are also focusing on making the network wireless only (easier to build infrastructure)
Comcast would much rather sell a dedicated fiber to a business with capital and guarantees.
Selling to the individual consumer doesn't make a lot of sense business-wise, because of the deployment costs and continued support costs.
Comcast is also abusing their status as oligopoly to gouge costumers financially and qos-wise, but if they're selling to a business that buys large quantities and has staff who's job it is to handle network problems, they actually like that (right up until that business threatens to compete with them in areas where said oligopoly is in place, of course)
The difference in divisions/people/tech/resources doesn't explain anything for me. They're both the same company with the same CEO, whether it's one business unit or a dozen. It's not like the executives are oblivious to how much money each unit is making and whether another unit could make more in place of it. If you're the CEO and see you could charge twice as much by doing retail instead of wholesale then you'd obviously try to do that.
Rather, the explanations I'm getting from the other comments seems to be that (a) regulators require some kind of reasonable wholesale to exist to third parties, (b) the big ISPs aren't planning to serve those markets anyway, so they're not missing out on any income by taking money from the last-mile ISPs. And as long as those last-mile ISPs don't try to compete for the same customers then they're fine.
Then you've not worked in large B2B companies before. Eg Apple pays Google money and Google pays money to Apple, any perceived public rivalry goes out the window as far as business between the two is concerned.
If you're the CEO of Comcast, you've never even heard of this small time ISP, you have far bigger things to spend your time on, and the "upstream" business unit of Comcast really doesn't care what you're doing, so long as your money's green. It's all business. See also: Netflix using AWS despite Amazon having a streaming video service of their own.