Question

Why would the early temple have been much like a house

Answer 1

possibilities can be that in those days, the structure of the garbhagriha was not given much importance as compared to the deity... also, ventilation system was not advisable as it was found that they required more sophisticated architecture

Answer 2

Early temples has been much like houses because at early times people do not had houses .the rich peoples had both money and big houses .they are the one who built temples like houses for the poor ones to live in.