There doesn't seem to be a continuous lactate sensor on the market. Lactic acid production and/or clearance are definitely useful data w.r.t. exercise (many training regimens talk about lactate thresholds) and also useful in in-patient settings.
No disagreement about AGC in the hospital -- there is a lot of lab/titration work in current clinical workflows for monitoring patient glucose levels.
There doesn't seem to be a continuous lactate sensor on the market.
They exist, a simple search will turn up a variety (how well they work is a different question). But see my sibling comment, they're banned from cycling competition.
Lactate's available in the internal engineering data of these sensors, just not something that anyone has wanted to spend the time or money to qualify with the FDA. It essentially comes "for free" due to the chemical reaction the sensor uses.