I get what you're saying, but the difference is that Saturday and Tuesday are days when you'd generally expect games to be played (although sometime in the 80s or 90s Tuesday seemed to replace Wednesday as the midweek day). Friday is only a fairly recent addition to the fixtures and it's almost always for TV (I know that our second away game against the new club was only played on a Friday because there were other games in Glasgow that weekend).
If there had been any joined-up thinking then we wouldn't have been given four final day away games on the trot, but then again, this is the SPFL we are talking about.