With an aging population, there's going to be a lot more people who have trouble with doorknobs (due to common arthritis and other impairments) than those who have kids young enough to be stumped by doorknobs but not levers (say 3-5 years old) or dogs who turn lever handles. (So maybe 10% of homes.) It's not a "few" people who have trouble with doorknobs - it's probably close to 20-30% of your overall population and maybe 30-40% of households.

E.g. it's about 1 in 5 Americans who are impacted by arthritis (of some form), plus you have people with repetitive strain injury and other non-arthritic conditions who will also benefit from lever handles. Compare that to the relatively small fraction of people in wheelchairs and this seems like a no-brainer compared to ramps.