I always used convetional oils throughout the 90s and most of the 2000s. Never had a lubrication related problem.
Then the auto part stores had synthetic oil on sale for the same price as conventional. I'll do that. Then I viewed the results , first hand, of the synthetics ability to keep an engine clean even if it wasn't changed on perfect 5,000 mile schedules. It was a "buffer" for me, when life got in the way and "I'll do it next weekend" crept in.
I could easily do the same thing with a conventional (really a semi-synthetic) oil of today. But I can still can find synthetic oil on sale for the same price as conventional, so why go back. Guess the sales marketing worked after all these years.
For the normal consumer, they want the cheapest quick lube change at the lowest price point most of the time. At least the oils being used are better now, no matter what they use (oils meeting specification implied).