At the risk of perhaps re-casting the conversation, I believe you will find the answers to this problem in economics and specifically in terms of the market driven supply/demand curves. I suspect there are real live economists on this board that can explain all this in terms of supply/demand curve shifts, market equilibrium, Veblen goods, Giffen goods, Game theory, etc etc etc. Would love to hear their insights on this.
However, from my non-academic, manufacturer point of view, it seems the dynamic for one cycle works like this:
1) Little or no broad based market demand for a specific UL product exists, so what little market there is, is satisfied individually by MYOG efforts.
2) As time passes, and MYOG efforts identify, iterate and improve on what the market really wants, starts to spread the word, and generates a larger demand.
3) Capitalists take notice of the larger demand and invest in raw material, inventory, tooling, trademarks, patents, logos, packaging, distribution chains, etc to build the MYOG item cheaper, in larger volumes/man-hour-of-effort and at a higher/more consistent quality level.
4) Repeat....over and over again.
The way I see it, once a large enough market self-identifies itself through the MYOG efforts, the capitalist community will eventually step in to deliver products into that space at an arguably better deal than you can pull together yourself.
Speaking to my narrow little Caldera Cone corner of the world, the price break, coating options, material property specification advantages we get purchasing hundreds of pounds of aluminum at a time over what you can get from Home Depot buying standard flashing is an advantage right there. Then the ability to quickly make a unique custom cone that can perfectly fit one specific pot in a field of 50 or so pots requires tens of thousands of dollars worth of tooling, machines, shop space and infrastructure that you couldn't justify if there weren't a somewhat established market to consume the cones. With respect to the cone, our tooling can do in 10 minutes for any random pot what would take a MYOG guy the better part of a weekend to do one time from scratch for a very specific pot.
In summary, I guess my point is that the MYOG effort is excellent at identifying and narrowing market needs at the one end, and giving the builder the pride of accomplishment in creating your own gear on the other. However, outside a fundamental upheaval in what we all think of as the stereotypical supply/demand driven marketplace where vendors step in as a market self-identifies, I see the 4 step cycle above kinda driving the behavior.