Cost of rubbish collection

I know that this question has already been asked but I'm not sure that we've had an answer.

from the ORDENANZA FISCAL RELATIVA A LA TASA POR PRESTACIÓN DEL SERVICIO
MUNICIPAL DE RECOGIDA DE BASURAS

ARTICULO 5º - CUOTA TRIBUTARIA.- La cuota tributaria será:
a) Tarifa Vivienda: 31,50 euros/trimestre
b) Oficinas y pequeños comercios: 63 euros/trimestre
c) Locales comerciales e industriales: 85 euros/trimestre.
d) Grandes empresas, hipermercados, discotecas y extras: 135 euros/trimestre
La cuota tributaria será en aquellas viviendas donde se presta el servicio de
recogida de basura que se encuentran en el Municipio de Orihuela y Urbanizaciones de
extrarradio (Sector D9):
a) Tarifa Vivienda: 50 euros/trimestre

You will notice that whilst houses in Bigastro pay 31.50€ per quarter for rubbish collection, we pay 50€ because we are classified as being in the suburbs even though the value of our land is the same as many of the Calles in the town for tax purposes ( 210.35€ per square metre).

The question is - why are we classified as "urban" for our Council Tax rate and in the "suburbs" for the collection of waste?