Word/phrase/name for the phenomenon where early adopters tend to end up behind because of their early adoption?

The word "leapfrogging" jumps to mind, with the canonical example of Africa having a much more well developed cell phone network as a consequence of having skipped the land-line telecommunications network development stage, providing a greater marginal benefit to adopting the cellular technology.

I don't think that's what's happening with hotel wifi, though - I think that's more of a different market where fancy hotels have less incentive to provide fast wifi and have less price-sensitive customers than those roadside motels. That why question is off topic for EL&U.SE, though.

For the transit example, I'd use leapfrogging or lock-in (from Lawrence's answer) depending on if I'm focusing on the area ("leapfrogging") or a particular company ("lock-in"), and also depending on what I wanted for the grammatical subject, which may shift a sentence's focus. (The early adopter is leapfrogged by the later adopter. The early adopter is not the one doing the leapfrogging.) I also might be more likely to use "lock-in" if it's due to contracts with a specific vendor, rather than a class of technology.

Informally, the early adopters are said to be locked in to what becomes old technology. Here's an example of this use:

• Heine says a growing number of advisers have clients effectively locked in to solutions built on old, inflexible technology, which is “a real problem for the broader industry”. - Old technology holding back development says netwealth, by Simon Hoyle

More formally, the phenomenon may be termed path dependence:

Path dependence explains how the set of decisions one faces for any given circumstance is limited by the decisions one has made in the past, even though past circumstances may no longer be relevant. - wikipedia

Strictly-speaking, path dependence doesn't necessarily mean that the early adopters "end up behind". As you note with your railway example, it is sometimes that "the existence of the older transit options prevents progress". However, in an environment where technology is improving, early adoption eventually means having adopted a line of technology prior to the latest improvements.

Here is a usage example of both terms together:

• Under such circumstances, the old firm might be considered "locked-in" to this inferior but still more profitable technology, exhibiting a first-degree form of path dependence. - S. J. Liebowitz and S. E. Margolis, Path Dependence, Lock-In, and History

This reminds me of the dialectics of lead or law of the handicap of a head start.

The law suggests that making progress in a particular area often creates circumstances in which stimuli are lacking to strive for further progress. This results in the individual or group that started out ahead eventually being overtaken by others.

Reference:
https://en.wikipedia.org/wiki/Law_of_the_handicap_of_a_head_start