Q. Why do synagogues all look so different?
A. First let me agree with you before questioning your basic assumption. We have synagogues that look like Byzantine churches, Islamic mosques, Italian opera houses, European town halls, British railway stations, and even aircraft hangars and cinemas (one congregation I know used to say they had a cinemagogue).
Synagogue architecture is often imitative, trying out every possible design and sometimes an eclectic combination of styles. Architects have tried to find a uniquely Jewish design for synagogues, but without much or lasting success. This cannot mean that architecture is too difficult for Jews, since there are amazingly talented Jewish members of the profession. In any case, some synagogues are designed by non-Jews who have researched their commission carefully, and it is hardly possible to accuse them of having an artistic blind-spot when it comes to synagogues. So I agree with you that there is a vast range of synagogue exteriors.
Internally, however, synagogues all have the same configuration, an inter-relationship between Ark, bimah, amud and congregation. The lesson to be learnt is that a synagogue does not have to be massive or, as has been said, “meshugothic”. Big or grandiose is not necessarily better. The Torah puts into the Divine mouth the words, B’chol hamakom asher azkir et sh’mi avo elecha uverachticha – “In every place where I cause My name to be mentioned, I will come to you and bless you” (Ex. 20:21). Even a modest one-room shtiebel is a fully fledged synagogue.