Actually, they are possibly rare. Rareness is a percentage, so as long as only 1% or less of planets are earth like, that's rare, even if there are millions of them.
Rare: if we take a sample of N random planets, only n << N of them will be Earth-like. E.g. 0.1% is "rare".
Scarce / few: if we take all the planets in the Universe, only a small absolute number of them will be Earth-like. E.g. 100 Earth-like planets is "scarce" or "few".
That is, Earth-like planets can be not scarce at all, but still rare. Much like while all water in Earth oceans contains 20 megatons of dissolved gold, molecules of gold are rare among molecules of water, which makes extraction of them impractical.