Why is my SSD hard drive not being read by Mid 2010 MacBook Pro

I can’t speak for Crucial on their drives specs. They don’t list SATA II 3.0 Gb/s compatibility in their data sheet. They only state SATA III (6.0 Gb/s).

Unlike Crucial Samsung lists full compatibility with their SSD’s Samsung 860 EVO SSD.

Your system is only SATA II (3.0 Gb/s) so you do need a SSD that is compatible with your system. A common issue with the MacBook Pro’s is a bad HD SATA cable. I do recommend replacing it MacBook Pro 15" Unibody (Mid 2012) Hard Drive Cable and yes this is for the 2012 model which offers a better cable design and will work in your system too. I also place a strip of electricians tape on the uppercase where the cable crosses over to help protect it from the rough surface of the aluminum. You also want to arc the cable not crease it! The thin foil wires within the ribbon can be damaged when you over do it!