You may be right, but in the circumstances, with a low number of POB, I would think moving the pax into a liferaft at L1 with other doors closed sounds sensible providing the aircraft is not sinking faster than you can board pax into the raft(s). It doesn’t take long to open R1 if the need arises. The practicality on a B737 is that to launch a second raft at R1 actually delays the evacuation of the pax onto the raft already launched at L1. The second raft needs to be removed from the overhead mid-cabin stowage, and carried down the aisle. This requires the aisle to be clear, so all pax remaining seated. Why would you waste time with that if you already have a 56 person liferaft launched at L1 (and a few dozen fishing boats circling your aircraft)?
It is also my understanding that Boeing now recommends all life rafts be launched one at a time through the front door(s), despite earlier recommendations that liferaft #2 and #3 be launched from the overwing exits. This presumably comes from analysis of the best chance of evacuating a full load of passengers, the estimated body angle in the water, and the possibility of raft rupture due to debris around wings. Looking at the body angle in this accident, I’d say they are on the money. The overwings start to flood while the forward exits are still quite clear of the waterline.