As a selfish Lifetime Titanium (LTT?) I am fairly happy to keep this as a grandfathered status and the maximum lifetime membership now as Platinum. I'm of the view that having a lifetime status of Platinum (mid-tier) in return for holding a credit card for a long time, and doing a reasonable number of hotel nights, is fairly sensible as an ambition for Bonvoy and most members. If you want higher status, hence higher rewards, go spend more time and money with the program (which is why I'm fairly happy earning Ambassador on a regular basis, but don't really expect a lifetime Ambassador status, even though I could probably achieve it).

The rationale for this is that, at least at the moment, Titanium has some value and rewards people who are being loyal to Marriott. However, when I earned that status it was with a pre-Bonvoy program that was be pretty selective. Earning Titanium (was at the time Lifetime Platinum in the old program) really did mean that I had spent over 1000 nights in a hotel and had earned 2+ million points, which was a lot of Marriott income.

There have been big changes with Bonvoy that make earning 1000 nights far easier, and are therefore make earning Titanium far simpler, and hence something Marriott shouldn't do because otherwise it would devalue the status for people who are, for the most part, spending a lot of time in a hotel (al-la Hilton Diamond, gotten purely through a credit card):

1. Credit card nights earning, that count towards lifetime status. At some point Marriott is going to have to address that people are earning 40nights/year (so 400 over ten years) just by holding a credit card. In 15 years you can get LTP without a single stay (this would obviously be fairly pointless in practice and bears no cost to them)
2. Bonus nights: I seem to remember "back in the day" Platinum was the hardest top tier status to earn as it was literally only managed with 75 nights in a hotel. You didn't even (unlike SPG) earn 3x nights for paying for 3 rooms. Now there are regular "double nights" promotions in the first half of the year that also count towards lifetime status. I seem to remember there were some instances in early 2009/2010 (Global Financial Crisis) when they counted your nights towards the next year, but I don't think they also counted towards lifetime status
3. COVID nights: I have probably received about ~150 lifetime nights due to COVID with the regular grants (I live in China, so got the final 50 nights in 2023). That is 25% of the way towards the LTP already, just because I was also able to maintain some travel/staycations during COVID
4. (You could potentially add a fourth item - that there are now way more Marriott branded hotels and options, so it is easier to earn status as more cities have such hotels available - you don't have to sacrifice as much to stay in a Marriott. I remember 500+ hotel nights where there was a closer/nicer hotel than Marriott to work, but I chose Marriott due to status and spent time travelling as a result)

You could argue "well, make LTT valid at 2000 nights" for example, but to most people that seems crazy, even as 1000 nights probably also seems nuts, and likely has a demotivating effect.