Installing Windows XP on 2000s Custom Built PC

Let's face it, Windows XP is the best operating system of all time! Majority of the computers in the 2000s run Windows XP especially in the late 2000s when Windows Vista was released, a lot of computers still run XP despite Vista is the latest version of Windows. So let's say it's the late 2000s, you build a custom computer and you want to install XP instead of Vista because well you know why. Even though (you know) this computer has a 64-Bit processor, you install Windows XP (32-bit) anyway (unless you use a x64 edition of Windows XP which is based on Server 2003).

Specifications:
Motherboard - ASUS M2N-SLI Deluxe
Processor CPU - AMD Athlon 64 X2 4800+ (2.5 GHz)
Memory RAM - 4GB
Video Card - ATI Radeon HD 2600 PRO (512 MB)
Hard Drive 1 - Western Digital VelociRaptor 300GB 10000RPM 2.5 HDD (OS Installed)
Hard Drive 2 - Seagate Barracuda 500GB 7200RPM 3.5 HDD
Hard Drive 3 - Seagate Barracuda 320GB 7200RPM 3.5 HDD

Question:
Why 32-bit was popular in the 2000s even though we have 64-bit processors like AMD Athlon 64 or Intel Pentium D? What about multi-core processors that are on the rise and computers in the late 2000s are equipped? That is also 64-bit (mostly) like AMD Athlon 64 X2 or Intel Core 2 Duo. Laptops were incapable having a 64-bit mobile processor until somewhere in the mid or late 2000s, which of course Laptops were popular as Desktop were becoming unpopular in almost entire 2000s. But despite Laptops having 64-bit mobile processor, Windows operating system (including Vista) still run 32-bit and not 64-bit (including Desktop) usually from OEM that people often buy instead of building a PC. Is it software compatibility? Comment down if you know the answer and I would appreciate it why we use 32-bit in the 2000s compared to 2010s and present where we use 64-bit instead.

Recorded on my Android Phone.

P.S.
1. This video was recorded in January 10, 2024 and it was left unfinished until August.
2. It's was uploaded after my channel restart.
3. I never had a thought of scrapping the video project.