Why haven't we detected any aliens?

I'd say we haven't detected any aliens because:

1) Life in the Universe will be very uncommon given that a suitable star and planet are required.

2) Even on those planets where there's life, life as intelligent as us will be rare.

3) Yet rarer still will there be intelligent life with limbs and opposable thumbs and living in an appropriate environment so they can manipulate their environment (which rules out a life form similar to dolphins even if they are as intelligent as us).  

4) And extremely rare indeed will there be intelligent life with the appropriate technology to make their presence known. Consider the percentage of time that human beings have had the appropriate technology compared to how long we've been on the planet.

5) And then they need to have a desire to create technology and manipulate their environment. For example, other intelligent beings might just like to swim in their oceans and play. 

6) Aliens might have found something better than electromagnetic signals to communicate with.

Considering all the above I'd have been astounded if we had of detected any alien signals!  So why do the "scholarly" community think it is strange we have yet to detect anyone?