Per the map at this site, virtually all of the states in the western half of the US offer both early voting and no-excuse absentee voting, except for a couple that sidestep the issue by having people vote entirely by mail. Some Eastern states also offer these options (or at least one of them), but it seems to be noticeably less common. There’s a visible dividing line on the map, running from the Minnesota / Dakotas border on south.
This isn’t the pattern I would have expected to see, if you’d asked me to guess: it pretty clearly does not map onto Democratic vs. Republican states, for example, at least not in any very obvious way. And, at least in the Eastern half of the map, there are some states that seem to have fairly similar demographics but very different laws. So, whence the pattern? My only guess is that it might have something to do with population density and people having to drive a long way to vote, but that is pure speculation on my part.