Author here: we did, and as other comments say we removed it in favour of Ignition, with the intent of at some point in the future bringing back some form of baseline compiler.

The big difference is that Sparkplug compiles from bytecode, not from source, and thus the bytecode stays the source of truth for the program. Back in the FCG days, the optimising compiler had to re-parse the source code to AST, and compile from there - even worse, to be able to deoptimise back to FCG, it had to kind of "replay" FCG compilation to get the deopted stack frame right.

We did actually have a configuration (never released) that had Ignition, FCG, _and_ TurboFan, and boy was it a mess...