Of course the technology exists to eliminate passport books and cards altogether and rely on biometrics alone. All visas and other travel docs could be "attached" to the biometrics file.

But, doing this requires pretty much universal agreement. If you show up at the German border and have not signed your passport, you won't be admitted? Who cares about signatures? Answer: The Germans.

When you enter Schengen, rhe rules are that your passport must be stamped so that it can be seen when you exit. A possible hassle if it is not done.

I am not sure that a cost-benefit analysis makes what you propose worthwhile even if were practical. Putting government employees out of work is not favored in many places.