There is more to it than not wanting to fly on grass, I think it goes back to why people learn to fly today.
I was obsessed with aircraft from the day I started School, My school playground ran onto the old Long Kesh airbase in Northern Ireland, which later became the infamous "Maze Prison" with the "H" blocks.
In 1961 when I started school it was a gliding site with the odd visit from a Cub or similar and a few WW2 wrecks for us to play in. I pestered the pilots to take me flying and at the age of 8 I had my first glider flight (without my parents knowlege). that was it I was hooked, and learned to fly at 17. No money but would work my ass off on the farm to pay for a flight.
Now, I think a lot of PPLs don't have the same burning desire to be a really good pilot. There seems to be a level at which they "have arrived" and don't want to progress any further. I hear things like, "wouldn't want to fly one of those old Cubs, look at the age of that" or "why would anyone want to fly a tailwheel". They buzz around the same bit of sky in the same spam can that they never really mastered.
That glider flight was 40 years ago and I am still obsessed and I will jump into anything with wings (almost) and will fly it until I master it and take it to the edge of the envelope, but that's me, and I suppose I find it hard to understand how other pilots don't have the same desire.
Tony