Well...its why we still fly behind 1940's engine technology
There have been significant improvements in piston engine technology since the 40s, especially in overall efficiency and reliability. Just go to any new car dealer today to see it in mass production quantities.
Light aircraft still generally fly behind 40s technology because developing and certifying improvements is expensive, and has only gotten more so. At least in the 40s and 50s, a lot of tech and knowledge could "trickle down" from work on big air-cooled engines used on transports. When the turbine engine came along and essentially replaced piston engines on everything it was economical to do so, much of the funding for aviation piston engine development dried up.
The later automotive-derived improvements like variable-timing electronic ignition, electronic fuel injection, etc. are stunningly expensive to certify, in large part because the applicable cert requirements were written to the needs of advanced-technology engines for airliners and ETOPS, and IMO are very much overkill for the needs of light aircraft. Plus, many potential improvements might be incompatible with leaded fuel (and we all know how well the unleaded fuel program is going), or require liquid cooling (a pain to integrate on airframes optimized for air cooling, or expensive to develop new airframes). With an anemic market barely holding on, nobody has the cash to burn to make something new and nobody wants to pay the massive premium to buy one unless they can amortize the cost in a commercial application (see diesel trainers).