The bqasic problem with cookies are that they require the client to store data on behalf of the server.
Cookies are identifiers generated by the server.
Each client must in the worst case store one cookie per site visited. Session IDs on the other hand provide tracking capabilities but cost only 16 bits of machine specific data. This is a very low margin business. The requirements for storage also mean that it is difficult to configure a portable to have the same configuration as a workstation. I would like to be able to access the web from my laptop as if I were continuing a session I started on the workstation.