Serotonin reuptake inhibitors (SRIs) block the action of the serotonin transporter (SERT) which, according to Wikipedia, leads to an increase in serotonergic neurotransmission.
Now this book summarizes serotonergic neurotransmission as follows:
[The neurotransmitter] binds to specific receptors on the postsynaptic cell, thereby generating a postsynaptic electrical signal [...]. The transmitter must then be removed rapidly to enable the postsynaptic cell to engage in another cycle of neurotransmitter release, binding, and signal generation. [Neurotransmitters are removed by] reuptake into nerve terminals [...].
So my question is the following: If, as stated in the quote, the transmitter must be removed rapidly, shouldn't an increased amount / binding potential of SERT actually be a good thing because if there are more transporters, the process of removing the neurotransmitter is much faster? And consequently, why would blocking the SERTs help in serotonergic neurotransmission? Is it because the neurotransmitter must remain in the synaptic cleft for a certain amount of time? Is it because the reuptake takes place before the neurotransmitter could bind to the receptors of the postsynaptic cell? Or ist there yet another reason?