Big Picture Science – Cosmic Conundra: Seth Shostak / Alien Megastructure?

If this is a red dwarf, if it’s a gas giant 3 Times larger than Jupiter orbiting it (and all that is quite possible) and if the giant orbits pretty close (as it often is the case), well sorry Seth, your structure goes bye bye.
Especially if we didn’t catch a single signal from a million Y.O civilization “only” 1500 L.Y away.
If it requested “the mother of all transmitters” to get these signals, why would SETI exist at all in the 1st place ?
Regards,