The problem
A blindfolded solve is two distinct skills sharing a single stopwatch. First you memorise the cube's state — a letter scheme, a route, a story. Then the blindfold goes on and you execute what you memorised, with no feedback until you take it off and find out whether you were right.
Those two halves fail for different reasons and improve at different rates. A solver whose memo is slow needs different practice from one whose execution is slow. But general speedcubing timers were designed for sighted solving, where there is only one phase, so they record one number — and that number cannot answer the only question a BLD solver actually has.
The workaround most serious solvers end up with is a general timer, a spreadsheet to reconstruct the split, and a browser tab full of commutators. It works, badly.