> wouldn’t the energy companies eventually do this, which, given macro market laws of supply and demand, would eventually cause the price of electricity to go dramatically down for their end consumer, thus eliminating the financial benefit of privately installed roof top solar for homeowners?
No, because your local utility is a monopoly, albeit a regulated one. Local utilities may be interested in solar if it generates supply at lower cost compared to legacy sources, but the cost of supply is completely independent from the question of retail pricing. Utilities are not required to pass savings onto consumers; in markets, pressure to do so is caused by competition, which is non-existent here because the utilities are monopolies.
So the question you're really asking is whether governments will use their regulatory power over utilities to pressure them into dropping prices as their costs go down. An optimist will answer you yes, political pressure will force regulators to force the utilities to pass savings along to the customers. A pessimist will answer you no, the utilities will come up with whatever reason du jour why they can't drop prices - rising labor costs, infrastructure maintenance costs, administrative costs, expansion costs, building up a warchest, whatever, and regulators will permit them to pocket the difference. A realist will answer you with a question: given that you have a stable price on achieving certainty / stability (the cost of a rooftop installation), would you rather pay the price to get stability or take a bet and risk losing some multiple of the initial outlay in the difference over the years you'll be a homeowner?
Given that homeowners are statistically more likely to prefer stability (comes with the commitment of signing multi-decade mortgages), it doesn't take much to understand why rooftop solar is popular among homeowners. Stop wondering about how people make rational decisions and start understanding that most people make emotional decisions and then use the online calculators etc. to justify the emotional decision they made.