Magen Avos on Yom Tov night (Shabbos 24b)

Rashi (d"h mishum) says that the Rabonnon were mesaken Magen Avos on Shabbos because of the sakana. They wanted to give the latecomers a chance to catch up so everyone could leave shul together so they added the tefila. However, during the week most people just davened at home after work so there was no need for the takana. There also was no takana made on yom tov but Rashi doesn't explain why.

The Sfas Emes says that it could be there was no takana because everyone was in shul on time on yom tov night because they never started early. On Friday night they were often mekabel Shabbos early but they didn't do that on yom tov. I was thinking that it could be that people were in shul on time not just because it started late but because people spend weeks preparing for yom tov and by the time it starts people are ready and are in shul on time. Whereas Shabbos has become a routine and people don't take it as seriously so they often come late.

Or the answer could be the opposite. It could be that yom tov was more like chol in that people didn't come. He quotes Tosafos in Taanis on 2b who (in talking about something else entirely) quotes the Yerushalmi that says that not everyone is in shul on yom tov night. If that's true then there would be no need for the takana just like chol. He doesn't explain why but last night someone suggested this answer (we hadn't yet seen the Sfas Emes) and he said that nowadays it's true. On Friday, people have it in their schedules to leave work early so it's easy to get to shul on time. On Erev yom tov it's often harder to get off from work early. You're about to take off two days in the middle of the week and to leave early the day before is hard. So maybe that's why the takana wasn't made.