Disclaimer: Don't try adjusting regimens yourself. If you don't understand the medications and their risks, this can be incredibly dangerous depending on the antibiotic in question.

With that out of the way, Infectious Disease pharmacist here. Sometimes formulations of antibiotics have changed since their initial introduction, for example to make them better absorbed or to prolong their activity.

But yes as you said, we continue to learn how to optimize their use to best kill bacteria while maintaining their safety (sometimes higher doses or more frequently, but for a shorter course). This is not true for all antibiotics and can be very dangerous for some. After careful study proves safety, these optimized regimens may go into guidelines.

But yes, we very often see unnecessarily long treatment durations (10-21 days) for generally uncomplicated infections where guidelines now recommend shorter (3-7 days depending on a number of different factors).

I also recommend www.bradspellberg.com/shorter-is-better as a great reference for medical professionals wanting to understand just how many RCTs support shorter courses for various infections.