Why 3072 bits for the key instead of 4096? I understand that they see a huge amount of connections to their systems every second, but this isn't the year 2008.

Why 3072 bits for the key instead of 4096? I understand that they see a huge amount of connections to their systems every second, but this isn't the year 2008. They have the processing power. Is it a decision based on "good enough"? Or some compatibility nod towards old abandonware still in use?