It's like trying to convince someone that there is great value in using miles over paying for tickets. Most people will come up with many excuses (don't have time, too difficult, not true, can never find the flights I want). They just leave more for everyone else.
Same with new vs. used, which is really different that buy vs. lease, but people can make whatever decisions they choose to make. Every new car buyer is one less used car buyer which leaves more for us.
It's important to note that there are no ironclad rules about the relationships between buying used, new, or leasing. Everything depends on the current state of each market. The reason I say this is because the tighter the used car market supply is, the smaller the gap is between used and the other methods.
For a significant period of time after Sandy, the used car market became very tight in the NY metro area, and it became less and less worthwhile to buy used. I was looking to buy used at the time, and I spoke to a family friend who is in the business (he has a body shop and buys/sells used cars as well). He basically told me straight out not to buy used as the values just weren't out there at the time. This is from someone who stood to potentially make money off me if he would have had something worthwhile. I leased instead (there were other reasons for that decision too, but I won't get into that).