One possible reason is because you're using a high DPI screen.
When programs run, Windows says "hey, are you high DPI aware?". If a program says "no", then Windows handles the scaling to ensure that they aren't microscopic. If a program says "yes", then Windows lets the program do the scaling.
Unfortunately a number of programs incorrectly say "yes" (when they actually mean "no") and, as a result, end up being displayed extremely small.
Previously you needed to change a registry setting and use manifest files to resolve this - however in the latest version of Windows you can now right click on the executable, select properties and override the DPI setting:
The options are:
- Application - The default setting, scale only if a program reports itself as not high DPI aware.
- System - Windows will stretch the UI, this will cause all text and graphics to become blurry.
- System (enhanced) - Only works with certain (GDI) programs but will scale programs whilst reducing the amount of blurring.
My recommendation would be to always try "System (enhanced)" first and fall back to "System" if that doesn't work.