"Why can't I buy shower heads that deliver more water than 2 1/2 gallons per minute?"
It is now a federal law that all showerheads sold in the United States must be low-flow.

"Do all of your heads deliver 2.5gpm?"
Yes, at 80 psi all do (unless it specifically states otherwise). If your house has less pressure than 80psi (while the head is operating) then you might get less volume than 2.5gpm.

"My shower head is off-center when it is tightened. How can I center it without leaks?"
Back it off until it is centered; then count the number of turns it takes to remove it. Reapply lots of PTFE thread sealing tape (clockwise), then thread the shower head onto the arm the same number of turns that it took to remove it.

"Do you sell a shower head with an easily removable flow reducer?"
Due to Federal energy savings laws we may not sell a shower head where the water restrictor is "easily removable."

"Does the showerhead I ordered swivel, or do I need an additional part for it to do so?"
It is rare for a showerhead not to have a swivel feature unless its position adjustment is in the shower arm or it is a "flat" model that is meant to be installed parallel to the floor. With the exception of those mentioned, some industrial models and most handshowers, standard-style showerheads generally come with a built-in swivel feature.