Why isnt Brook calling out Mayweather?

[Scipio2009]

I dont get why he is not calling mayweather out for the fight in September? Or did he? He keeps calling out Khan like no tomorrow, but why not freakin floyd? He has a belt, his win over porter was solid, he most likely wont get the fight with floyd even if he calls him out, but he has a legit case to fight him.

Because there's no need for him to call Floyd out, especially if the aim is to actually get the fight:

-Brook's promoter, Eddie Hearn of Matchroom Sport, has a solid working relationship with Al Haymon, Floyd's adviser.
-Matchroom Sport apparently has the exclusive right to put boxing events on Sky Box Office (biggest fight in UK history apparently generated near 20m british pounds on Box Office in the UK, equivalent to about $30m in additional revenue for the event)
-Brook, as an unbeaten welterweight and the only other full champion in the division, understands that his name in the mix (unless Floyd really does pull a "Rod Salka"-type fight, the only names really left in the hat are Kell Brook, Amir Khan and, now, Shawn Porter)
-Brook is already positioned to get a big fight event, with or without Mayweather, for around that same time period

Brook will let his promoter do his job, and leave things to that; the Khan talk is simply because he doesn't like Amir, Khan-Brook is arguably the biggest welterweight fight in British history, and Khan has thrown out every excuse possible to avoid him.