One reason would be that you have a future (years) ship date and aren't yet in full production (but close). The sooner you adopt the new environment art and lighting workflows, the less sunk cost you'll have in assets/workflows that are now irrelevant.

There are also staffing implications. If you no longer have to create LODs for your environment art, do you reprioritize your environment art outsource budget? Likewise lighting, if we can hit higher quality with 1/3 of the personnel, where does the budget then go to? The earlier you can get a handle on the implications of these new workflows, the better you'll be able to answer those questions.

Because your particular project might really benefit from one or more of the new features?