"Much more forgiving"? Not always. This thread has concentrated on the merits of grass runways, and on denigrating the pilots and instructors who avoid it. That's fair enough, but it's worth looking at the downsides too.
The major issue with a grass surface is not that it's green, but that it can be uneven. Surfaces vary, from the "billiard tables" to the "rollercoasters", so there's obviously no standard, but even the finest grass surface has the potential of hiding a rough patch that you wouldn't find on a tarmac strip. I say "potential" because you can take-off and land on a grass surface 100 times and not find the rough patch. But looking at accident rates overall, 99% success is not great!
Uneven may not be a problem -- it's very dependent on the aircraft. Having spent 10 years flying a Mooney with a very stiff undercarriage and minimal prop clearance, I can vouch for it being a problem for some. That's not to say that you can't operate a Mooney off grass -- you can, but the risks of an expensive but knock are higher.
Crosswind take-offs (in particular) also seem to be more challenging on grass. There you are ten knots below rotation relying on a little lateral grip from the wheels and ... whoops... the wheels just lost contact with the runway.
When you get to twins, it starts getting serious quickly. The
Seneca fatal accident at Newmarket was almost certainly a consequence of the surface. A prop strike on take-off in a twin is more than just expensive. Again, you can operate twins off poor surfaces, but it's important to think through the downsides.
Overall, I think that makes it even more important that pilot training includes some operation from grass, to build appreciation that it's different. Grass is great, but let's not take it for granted.