That's not entirely true. It was done for the following reasons.
1. To save money on the deadheads because they would used to have to send three Trains from Concourse Yard Friday evenings to 135th Street spur and deadhead to 174th Street Yard which also caused delays. Same vice versa on Sunday Nights
2. Because the Train shared its R32/R38 Equipment with the , it was easier to swap equipment if needed. It was also easier to do maintenance and work on the equipment.
3. Easier for the to used each other equipment if needed.
4. Weekend Trains was initially supposed to run OPTO with R44s since weekend Train service used to run 4 Cars R32/R38. That plan was scrapped and weekend Trains were extended to 8 Cars.