Actually quite the opposite is true.

Styrofoam seems easy to repair because a bit of white glue bonds the pieces together.

The problem is that only "lucky" damage is repairable. All to often those foam beads go flying off into the wind leaving large gaps.

You quickly end up with a plane that looks like Frankenstein, and weights far more than the original.

With balsa you can fabricate your own replacement parts long after the manufacturers stop producing the plane and replacement parts.

Covering is easy to replace, and the end result is that there are 30 year old balsa planes flying today that look brand new!

With foamies, you'll get a few seasons at best.