Allowing old devices without those TPM requirements to work would not limit security of the devices that can work with it.
Sooner or later, these non windows 11 compliant machines will mostly disappear from most households and offices and will only attract retro computing and linux users when they will not match the usual memory requirements of the day. These are usually the kind of computers that came with 8GB or less of memory out of the box and they could quietly drop support for them somewhere later within the next 10 years when everybody is running 128GB of ram or so and only a handful of people care about it.
I'm fairly sure that you'll be able to run W11 without a TPM for a relatively long time, it's just not supported. It's a risk you have to take, it's a requirement for OEMs not to shaft you with the hardware they sell.
If anything it's the CPU requirements that create a hard requirement for newer HW. But in that case, that support is a cost for them. Why should they spend the effort for what is likely going to be a very subpar experience?
Sooner or later, these non windows 11 compliant machines will mostly disappear from most households and offices and will only attract retro computing and linux users when they will not match the usual memory requirements of the day. These are usually the kind of computers that came with 8GB or less of memory out of the box and they could quietly drop support for them somewhere later within the next 10 years when everybody is running 128GB of ram or so and only a handful of people care about it.