What difference does it make? It works. Many older recip aircraft didn't have
doors that completely covered the gear. The 737 is just the only jet. (that I
know of). It allows more useable space above the gear wells and is lighter. The
increase in drag doesn't appear to have affected it's performance enough to
matter to the hundreds of operators and there's several less parts to cause
trouble, cost money and decrease reliability. Sounds like a win win situation.