UI design is more often than not made harder by the burden of having to resize windows. Responsiveness is a huge issue users impart on developers. Thus, this letter calls to keep your window in conventional aspect ratios (ideally, a constant one we can set).

Remember when you reach for the edge of a window to drag it out that you aren't resizing your window, you're resizing our window.

More auxiliary issues exist:

Personalization is personal. People who prefer the apps at different sizes will have different experiences navigating the UI. This wider attack surface can create unforeseen problems, and it can also confuse users and dirty otherwise pristine interfaces.

If your UI library gives the capability to people to make their apps truly theirs, it will interfere with our plans for the apps.

Differences in distance and size may confuse people looking at screenshots of UI's. The human mind works like xdotool, and instructions like "720px, 140px" are more readable than "Next to the save button"

This is why we ask respectfully that our windows not be resized. They are built and tested for 16:9 1080p, and occasionally phone aspect ratios. Different sizes and layouts will make the application look different.

Though we are working towards the initiative of restricting resizing functionality in GUI libraries, this issue can not be dealt with in its entirety right now.

The challenge we face is that users launch our apps with the expectation that they will be able to drag it out or split it with another window. And a broader idea of aspect ratio flexibility, this has never been completely true.

If you like personalizing your window sizes. We have nothing against that, however, if your UI goes haywire deviating from the supported aspect ratio or size, it should be fixed on your own accord.

Graphical Displays and corresponding software for them should stay at one fixed size, instead of varying sizes. Solving this issue is very complicated and would damage many forms of accessibility, but devices varying screen size widely is also bad.

If you are a shipping hardware with an unconventional window size: first consider that you are not shipping your default software on that hardware, you are shipping our software on that hardware. Microsoft and Apple usually do not allow their software to be warped in such ways. And your actions are damaging to not just your users, but us.

We understand the desire for personalization, especially on platforms people use to have more flexibility such as linux. However, when you drag "your" window out, you take away power from us. It forces us to consider more edge cases and write more code, when things go wrong it forces us to make more bugfixes. Just because we use UI libraries with the ability to resize does not mean we are okay with you resizing our windows.