[Avodah] shir hamaalot

[Micha Berger]

On Tue, Feb 01, 2022 at 10:52:36PM -0500, Joel Rich via Avodah wrote:
> MB (3:11) points out that shir hamaalot is said before birchat hamazon on
> Shabbat (and non-tachanun days) in place of al naharot bavel. So how did
> the replacement become fixed and the original ISTM become abandoned?

I thought it was simply that a minhag to say more on Shabbos or Yom Tov,
often after a heavy se'udah, is more likely to be honored than a minhag
that costs time on a workday.

Tir'u baTov!
-Micha