Setting aside, for a moment, the rather explicit ageism in this whole discussion, and the likely selection/sampling/confirmation biases involved in coming to the idea that the upcoming game design doesn't interest a particular age group...
The argument for a product "for older gamers" largely becomes an argument that WotC should do what they have done before. It is an argument for retreading material and maintaining the status quo, and against innovation and new things.
It is also an argument putting short term income against maintaining long-term viability. The issue isn't that, in 2024 older gamers won't spend money. It is that gamers apparently age out of the hobby, and will stop spending sooner regardless of what the game looks like.
If gamers age out around 60 years old, then courting a 50-year-old gamer is courting 10 years of income, while courting a 20-year-old gamer is courting 40 years of income.
And, we can also note that (to use the vernacular names for the cohorts), Gen-X is a smaller generation than the ones who have come after. Even if these older people have more disposable income (which is arguable - younger folks seem to have money for videogames, which aren't cheap), you can make up for that with volume.