The rails were designed when all manufacturers had proprietary rail systems. The M was discontinued before it had time to become popular and have a manufacturer mount lights or lasers to the mount.
There is/was an adapter to convert the rail to picatinny but it isn't the most elegant solution. Notice how low the light switching paddles are in relation to the triggerguard.
It is too bad that the companies that produce laser mounted weapon sights never took advantage of the M-series rail system I think it would have made for a very firm fit of the unit to the frame of the pistol.