The shared footpath under the bypass ends at the bottom of Loanhead Rd and then there is no suitable connection into the Straiton Retail Park area.
Loanhead Rd is very steep with fast cars. Straiton Rd is fast dual road with unconnected bits of narrow painted cycle lanes. Both are total barriers for other than high-risk extreme sports enthusiasts. No way families could cycle to the shopping centre here.
The connections into Edinburgh (Burdiehouse Burn, or the new Loanhead-Lasswade path) are actually really good, so it's particularly sad that you're dumped in a car hell on the last few hundred metres.