There was a significant reason for the lack of more transformers...money. Bay didn't have anywhere near the amount of money needed to expand further. He said this many times that he didn't want to skimp on detail of the actual transformers and the "realism" he was trying to portray. That is why my quote above about the sequel specifically makes mention that the next one will have a much bigger budget. Thus, all of your issues with underdevelopment and not as many bot on bot action as you would have wanted will be squashed in the next movie.
It is great for what it is, introduction and a movie that sets the tone for the sequel.







