if they are willing to give such a good simulator away for free, why not show off the source as well?
Because giving away the source code to their simulator doesn't make any business sense in the way giving a Linux kernel driver does.
Giving away LTSPICE is an effort to commoditize their complements. The complement to an opamp is a high quality simulation model. The complement to a high speed data converter is a working Linux driver for JESD204B. Both decrease the effort involved for ADI's customer to use ADI's parts.
Giving away LTSpice source code doesn't achieve a similar aim.
Because giving away the source code to their simulator doesn't make any business sense in the way giving a Linux kernel driver does.
Giving away LTSPICE is an effort to commoditize their complements. The complement to an opamp is a high quality simulation model. The complement to a high speed data converter is a working Linux driver for JESD204B. Both decrease the effort involved for ADI's customer to use ADI's parts.
Giving away LTSpice source code doesn't achieve a similar aim.