No. But if the maintainer is burning out and doesn't have free time available for it, paying them so they can take time off to actually work on the thing is a nice way of fixing issues.
Besides, the maintainer in this case was already taking time off regularly, not to work on xz, but to get away entirely from any kind of programming work. Throwing money in his general direction probably wouldn't have helped with the burnout, unless you were offering to help him hire somebody.
Of course if the developers don't want to be paid, then that's that. But otherwise, there is a very heavy atmosphere in the open source community of excommunicating anyone who dares to ask for payment as heathens of the vilest order.
I fully agree that forcing payment or using dual licensing is unfortunately heavily frowned upon. But a voluntary Patreon/donation option is perfectly acceptable to the same anti-payment people.