Although everyone has a different "favorite" lens, the 24-70mm 2.8 lens usually ends up being used the most. It's standard zoom range and fast 2.8 aperture makes it usable for almost any type of photography. Today, I'm comparing the three most popular 24-70mm lenses to determine which one is...
fstoppers.com
You can see that all have their own disadvantages, either the size or the optical quality or the IS system itself.
So yes, they have waited until they could do one for the new mount, that is not too big while also being optically better than the EF 24-70 2.8 II
All the other FF mirrorless competitors (Nikon, Panasonic, Sigma, Sony) have decided to
leave out IS from their 24-70mm f/2.8 lenses and rely on IBIS instead, which suggests that it isn't easy to do.