Because CH341A drivers are unsigned:
Version 2.1.0.13 includes definitions for: asprogrammer 21013
Advanced users have compiled firmware for Arduino Mega 2560 to act as a programmer. ASProgrammer 21013 can communicate with these via custom scripts, though this requires manual configuration. Because CH341A drivers are unsigned: Version 2
In the software development lifecycle, not every update is an improvement. After version 2.1.0.13, later versions (2.1.0.14, 2.1.0.15, and the 2.2.0.x branch) introduced bugs related to: As a result, 21013 became the "frozen" stable standard
As a result, 21013 became the "frozen" stable standard. If you search for "ASProgrammer 21013 download" on tech forums, you will find pinned posts stating: "Do not upgrade beyond 2.1.0.13 unless you have a specific need."
The ASP21013 hardware is designed to function specifically with the AsProgrammer software (and its derivatives like AsProgrammer 2).