Is there any reason why YIZKOR in particular, should be said in shul (the synagogue) rather than at home?
Why is it common (orthodox) practice that women who almost never attend Shul make an extreme effort to come to shul for Yizkor?
According to this OU article, Yizkor can be said at home:
Why is Shul So Crowded? Can Yizkor be Recited at Home?
It’s ironic that shuls become extra crowded because of a prayer that doesn’t need to be said with a minyan!
It is not uncommon that people who are not regular synagogue attendees will appear on days when Yizkor is recited. There’s nothing wrong with this; it’s neither inconsistent nor hypocritical. It’s actually a wonderful thing that those who are not regular worshippers are willing to go the extra mile (sometimes literally) on behalf of relatives who are no longer with us. If anything, serving as the catalyst for their heirs to attend shul is a merit for the deceased! But if one cannot make it to shul, Yizkor can (and should) still be recited.
I've bolded a part in the above paragraph as this is, according to the author, one reason why many people attend shul for Yizkor.
My thinking is that there may be other influences:
Mishnah Berurah, among other sources mentions the importance of donating charity on the festival days, not just on Yom Kippur (read the article for its mentioning of this.) It's possible that a shul appeal may be a motive for people to attend and moreso, to donate. Public "pressure" to donate does tend to work well. (If you didn't hear about the shul's appeal, seriously, would you donate to the shul? Perhaps, yes, but not as quickly.)
Many people find it hard to mourn / memorialize on their own. They also may not be sure about what to pray or say, even with a siddur available. Many shuls make a "formality" of Yizkor. E.g., the rabbi makes a themed sermon; the chazzan sings a stirring tune; congregational / responsive reading, etc. Even if there is none of that, being with fellow mourners tends to make things easier for people.
Among non-Orthodox people, I've noticed that there is a general trend of many to associate shul with the dead. I.e., other than High Holidays (and even that's quickly dwindling), people will come to shul only for Kaddish (yes, I know that you need a minyan for that, but, the "nice" thing would be to "reciprocate" when others have to say Kaddish and the shul always has trouble getting a minyan.) and Yizkor. I asked a MY question about this phenomenon, a while ago.