Seems also I read that at least 3GB of RAM is required to run at 64 bit.

I'm not an expert in the subject but if the TV has only 2GB of RAM the OS doesn't need to be the 64 bit version.

The "WHY" is a down variety of things, like economics, time to market, R&D, like the manufacturer of the CPU not creating a full 64-bit software suite (aka SDK), Android having the Graphics drivers coded in 32-bit only nullifying the need for a TV to be in 64-bit mode, etc.

Maybe with TV's progressing to 8K as main stream we will see the more widespread adoption of 64-bit, but if Google doesn't progress the video driver development at rapid pace then TV's will continue to be 32-bit for the next 4 to 5 years.

As I said in my other comment, the device is running 64 bit due to memory usage. One thing I'd like to note, however, is that unless it's running a really old Android version, it's likely running a 64 bit kernel & a 32 bit or hybrid userland. This is what is commonly done for the low memory 64 but chips on modern Unix kernels where 32 bit emulation is supported on the processor - not only do you get the benefits of 64 bit on the kernel level, but also you get a more developed & tested kernel (32 bit kernels in general are falling behind)

This has been done on Android for years, & since Android 8 Android has supported a hybrid mode for the userland too, & in Android 9 it's required. So, don't worry about it too much - if you're on 8 or above you're likely running a 64 bit kernel & hybrid userland, with only the Android apps themselves running in 32 bit, which is a good compromise for a low memory 32 bit device