I'd presume that the commercial hull doesn't exactly hold on all that long. Also, the Floreals delivered to Morocco were ultra-cheap lowcost units. And of course they lack any kind of air defense or ASW capability, getting more important when considering increased difficulties with Spain or the old difficulties with Algeria. Also, it's not like Morocco can really use the big plus of the Floreal - its freaking huge range.
Besides, the replacement is quite a bit in the future. The FREMM likely won't be delivered before the mid of the next decade (optimistically 2012, i doubt it), the three Sigmas would enter service sequentially, first one not before 2012 (as stated by Damen).
The Descubierta would be 30 years old by then, the two PR-72 corvettes a bit older even. Other patrol units are getting pretty old too, with only partial replacements planned.
In the medium term, they could even keep the Floreals in addition as long-range patrol units, while retreating them from any frontline duty (that they weren't built for anyway).