Subodinate CA Key Length

Hi all,

After looking through all the public certificate (Eg. DigiCert,GlobalSign), I notice that most of the subordinate CA key length is 2048 bits.

May I know why nobody is using 4096 bits for subordinate CA ?

If I were to use 4096 bits for my internal Root CA and Subordinate CA, what is the impact that I may need to consider ?

Thank you