Quoted from northvibe:

From a business standpoint, unless producing old full board sets is cheap, why not convert all vaults to spike 2. Save money and inventory on building and storing transformers, wire, boards, light sockets etc. just think, why build two different cabinets, 2 different board sets, 2 different power setups, etc etc. it doesn’t make sense for them to keep building vaults with all original parts...

Quoted from northvibe:

It is refactoring current code to a new hardware. The code was already complete.
Remember they already have done this with a walking dead, iirc.

Quoted from flynnibus:

They didn't really... what the reference to was TWD was used in development of Spike. TWD was shown at shows to demo the new boardset. So while they did do porting of existing application code for that game.. it wasn't done for commercial reasons.
The modern games are developed like you would expect modern software to be.. an OS, a platform that provides base functionalities, and application code. There should be a reasonable hardware abstraction provided by the platform/base level so that re-use value would be high and to streamline game code development.