One still has to do field work to gather all the linguistic data. It's rather easy with settled societies only. Researchers studying indigenous languages had to

One still has to do field work to gather all the linguistic data. It's rather easy with settled societies only. Researchers studying indigenous languages had to travel to hard to reach places and often live with the tribes for a quite long time. It's a lot easier nowadays, but ease of transportation also correlates quite well with a levelling of linguistic distinctions. That's a problem because the comparative method of reconstructing older stages of a language relies on the assumption that different dialects maintain aspects of the older language.