I haven't heard why, but I believe the Turn lockout (note not loot) was done before CT was implemented but CT's loot lockout system was in effect made because of complaints over the Turn lockout system.

Get a good piece of gear per week, but able to run multiple times etc.?

For Coil T1-5 they are making it so you won't be locked out but I don't know about the loot situation. Perhaps they'll change it similar to CT's?