Answer

Hello A.,
Questions of this kind are problematic in my view, because they assume in the subtext that Jewish law is everything and that everything needs to be solved halakhically. I do not think there is a halakhic obligation to make a synagogue, or any other institution, accessible, and that does not mean that from a human and moral standpoint there is no such obligation. Of course, everything can be brought under catch-all clauses like “love your neighbor as yourself,” but it is difficult to derive from that a concrete halakhic obligation. And in general, the question is: on whom is this obligation incumbent? On each of the worshippers? Why should he invest his own money in accessibility for someone else? (Of course, whoever does so is doing something positive, but imposing an obligation is not the same thing.) An obligation on the state? On the community of worshippers? In my opinion, there is no such obligation. But of course there is an important human and moral value in doing so, and in my view that is enough. Think about it: is there an obligation on the community to fund medical treatment for a sick member of the community? There is an important moral value in that, but there is no moral obligation. One can put this under the heading of charity, but it is doubtful how far one can justify charity for religious purposes (so that a person can pray). Here, however, there are also social aspects (coming to the synagogue means being part of the community).
For example, there are views in Jewish law that there is no Torah-level prohibition against robbing a gentile. Does that mean there is no problem with it? Of course there is. Does that mean there is a halakhic deficiency on this issue? Absolutely not. Jewish law sets norms in certain areas, but there are other areas that it leaves to morality and to society’s determinations. It does not see itself as obligated to intervene in everything, especially not in moral contexts. If there is a moral obligation, there is no reason to impose a halakhic obligation as well (see column 15 on my site about this).