Why are there more negative feedback loops than positive feedback loops involved in homeostasis?

Because it is so much more important to be able to shut down a  process quickly if conditions leave the optimal range.

For example, if a cell's temperature is raised, a host of heat shock proteins are upregulated and shut down further protein production, protect the proteins that already exist and protect the machinery that is in the process of making new proteins.  Once this cell goes into this type of "hibernation"  it can restart its growth again at any time, once the temperature goes back down to normal.  It's not so important that the cell "snap back" to normal growth as quickly as it upregulated the heat shock response, because at that point, the cell is *leaving* a dangerous situation and not entering one.