If you mean WHY instead of WHAT, then I cannot explain since the instructions for these regulators is pretty clear about how to mount them and it is NOT the way yours is done.   I wrote about this before elsewhere so I won't repeat it.. my story is:

My original propane regulator, installed by Scamp, has failed after only 25 months, evidenced by propane escaping from the large (secondary stage) vent. It was mounted by Scamp uncovered and with the second stage vent in the vertical position but everything I read says that the vent should be pointed down, within 45 degrees, and/or covered. I have little doubt that their choice of mount contributed to the short lifespan of the unit.

• Should I get a similar model and install it as shown in the second photo (with better hose routing than is shown)?
• Or should I buy a model with a 2ed stage vent at the nine o'clock position (like in the third photo) and mount it on the side of the frame?
• What about brand? Marshall Excelsior perhaps? Or does it make little difference?
• Should I buy a cover for the second stage. first stage or both?

Edit: The covers for the Marshal reg are less than $7 for both so thats an easy decision.

PS.. This is not the post I made but instead just part of a series of posts I linked to.  There was more to it but that was edited out without my knowledge. 

Suffice it to say that the propane regs need to be mounted with the vents facing with 45 degrees of down, or covered.  Straight down is best and down and covered is fine.