ASLRing text segments is optional, but possible. There are negative performance tradeoffs.

Windows uses relocations, not PIC, to enable different load addresses. That means the image in memory has its self references patched by adding the difference between compiled in load address and runtime load address. System DLLs can still share code with one another as long as they share the same load address in different processes for that reboot of the operating system.

Historically EXEs were either linked without relocations or had relocations stripped. They were always loaded first so ended up where they wanted, no relocation necessary. But /dynamicbase flag to linker opts in to setting a bit in the PE header and retaining relocations, so the EXE can be loaded elsewhere.

TL;DR: Windows supports ASLR on both executables and dynamic libraries.

Gcc these days compiles with -pie (Position Independent Executable) by default. This makes the text section position independent and able to be relocated, like a shared library.

You are correct that the main TEXT section used to typically not be position independent.