Buglover. Common theme/question by you here. An accurate sticky of some sort for this regular question would be good.
I'm no expert but do have a vacation Rental house, so my free 2c - that is probably worth less!!!!
Legally anything under 6 months is seen as short term and so should be a "Hotel rate" and incur 9% Hotel Tax (like many laws here it is up for interpretation and bending by some!!!).
Short term lets are generally set up for nightly/week stays and have set rates that are around the same for a week as a long term is for a month. There is more involved in setting up Vacation Rentals than long term rentals (fully furnished, linens, towels, housekeeping, advertising, Tourist Board inspection and licensing, staff etc) that increases costs, so people with short term rentals shy away from accepting long term lower rates unless they have little to no choice.
You also happen to be looking at High Season when people will usually have quite a few bookings by now and only three will bring them the same $ as your rental. Long Term renters want a minimum of 6 months security. Therefore this is a hard period to find at long term rates. Not impossible, but if responses and progress are slow could help explain why.