There is a lot of grandfather worship in what some builders do.
That's not exclusive to homebuilts--give the systems parts of the certification standards a good read sometime.
I think what happens is that someone comes up with a good/simple/effective way of doing something on an airplane, that's better than other ways that are feasible
within the limitations and assumptions valid at that time.
Over time, especially if the pertinent technology is relatively stagnant, that way of doing things becomes the
de facto industry standard, maybe even becoming part of the certification standards. If the underlying assumptions don't change for a while, people and industry gradually forget the reasons
why it became the standard in the first place--"this is the best way to do it right now" becomes "this is the best way to do it", which in turn becomes "this is how it will always be done".
That's all well and good so long as the assumptions and conditions continue to hold true. But when something comes along that changes or invalidates those underlying assumptions--whether it's new knowledge/understanding, or a new/better technology, or something else--you have a problem. Sometimes it's a regulatory issue--a really simple example is 23.1557, which requires all "reciprocating engine-powered airplanes" to have their fuel filler openings marked with the word "Avgas" and minimum grade, which was great when all piston airplanes burned avgas exclusively. But these days, not all piston-engine airplanes do--if my airplane has a diesel engine and therefore runs on diesel/Jet-A, I've got a problem, albeit one that is relatively easy to get around.*
Now that's a simple example, but when you start looking at more complex things related to avionics, or to engine control, the waters quickly get muddier and hotter. In the interest of civility I'm not going to get into specifics, but I'm sure all of us here can think of cases where an older, established practice has been put up against a newer one. I'm not saying that the new practice/method/technology must necessarily be better--I just ask that, before immediately falling back to the older "proven" practice by default, take a moment to ask yourself a couple of questions: Why did this method become the standard? What made it better than the other ways? What things were taken for granted or assumed then that aren't now? What has changed between then and now? and If I didn't know about this older way, and was trying to start from scratch today, how would I do it? Do some research if you have to. If you really sit and think about it, and answer yourself honestly, you might change your mind. Or, maybe you won't. Either way, you've learned something
And now, you're making an informed choice rather than blindly adhering to the past or slavishly following the latest trend.
* I bring this example up because it's one of the many things we've run into in the ASTM groups looking at the new Part 23 standards. It was relatively easy to fix, but we've run into a whole bunch of situations where the question to the FAA participants of "well, why is that the rule? It doesn't make sense/is outdated/is based on assumptions that aren't valid any more" is met with answers like "well, when we wrote the rule 40 years ago nobody imagined there would be another way to do it" or "well, we don't really know why it's the rule, but we're sticking to it". Nobody has been able to explain to any degree at all why position light lenses need to be "flameproof" but landing lights need only "not present a fire hazard", but they won't consider changing it, either.