Why don't TBS deliver PKCS12 certificates?
To understand why TBS does not deliver PKCS12 certificates, on needs to know the difference between PKCS7 and PKCS12 formats.
A PKCS7 file contains the certificate and the certification chain while a PKCS12 contains the private key in addition to the previous elements.
TBS INTERNET NEVER knows your private key. This key is created with the CSR and is stored on your server. Its inviolability guarantees your exchanges' security. That's the reason why it can never be communicated to third parts, no matter what.
To generate a PKCS12 we'd need your private which would therefore be compromised!
QED
Generate a PKCS12 from a PKCS7
However, you can generate a PKCS12 file from your server. See:
Keybot: The exception to the rule
Our new tool, Keybot, usable from the order forms, proposes to generate private key and CSR for you, to store the first one on a secured area and to give the second to us for your order process.
When your certificate is ready, it is then delivered with its private key (according to the option you chose during the order).