Because scale matters. Things that are acceptable when they're difficult and expensive become unacceptable when the cost drops towards zero. When you can do t

Because scale matters. Things that are acceptable when they're difficult and expensive become unacceptable when the cost drops towards zero. When you can do things broadly and cheaply, you tend to do so just because you can. This is analogous to "data mining" in "big data", aka one major issue with modern science -- when you look at everything trying to identify basic patterns, you'll have a heck of a lot of false positives.