I think its useful to remember this is Codies first F1 game (they didn't actually develop the F1 2009 title). Its not unusual for first attempts to not include a safety car - I don't remember a safety car in GP2 for example and have iRacing added a safety car yet?
Safety cars do of course influence the outcome of a race, but having driven behind a safety car in GTR2, it is incredibly boring. And GTR2s implementation was pretty simplistic - I could overtake with nothing more than a verbal warning. I'm not sure if people expect the detail of safety car lines on the track (Hamilton at Valencia) or 10 car length rules (Vettel at Hungaroring) but coding a safety car won't be easy.