Its all to do with
Lift = Cl 0.5 rho V squared S
Swept wings (as explained above) are designed to reduce drag in the transonic speed range. The down side is that they actually produce less lift at a lower IAS. Hence your light A/C don't have them (and turboprops).
If you apply this to the above equation, with equal air density, speed and surface area, a swept wing requires a higher Cl than a straight wing. This means a higher angle of attack, which (in this situation but not always) means higher nose attitude.
EK