If it's about address collision, they wouldn't only search within a limited private key range that's quite possible to bruteforce.
If one has, let's say, 10 pigeons sitting in 9 cages he may search withing a limited number of pigeons (let's say at least 2) sitting in one cage.
The same is true with search within a limited private key range.
They still have a chance to find the key collision when searching "within a limited private key range".