If indeed the OP's booking for two was refused because only tables for larger parties were left, then wouldn't it have been better for the restaurant to say exactly that? Being told they were "fully booked" and "they have a lot of repeat bookings and are pretty full by the beginning of the year." really does suggest there are no tables left which was obviously not the case.
I understand that hospitality venues need to make a profit and in some areas are struggling, but they need to remember that couples are a big proportion of their 'bread and butter' all year. Without that custom they won't survive for the Christmas 'jam'. Tell the truth 'sorry but our tables for two have all been booked, we only have tables suitable for larger parties left' is honest, accurate and less likely to alienate anybody.
How will things change if our summers keep getting hotter
