Because if you have bitcoin and fiat to pay for that coffee you can
- spend the fiat and basically do nothing for adoption
- buy bitcoin with fiat and pay with that coffee with LN, you still keep your previous stash intact and you use the fiat you were spending anyway
I usually see you write potent arguments but what you just said seems to me to be a joke. It had to be at some point, I guess.
The growth of LN and Bitcoin adoption has to come because of a demand and a need for real usage, not because some Bitcoiners try to increase usage in an artificial way like that.