Because the house should not be cleaned during Tet, according to many local people.
Don't you clean before Tet? I was thinking the Vietnamese in Washington did this when I was growing up, but I might be confusing this with a Chinese New Year tradition.
You are right, before Tet, everyone does do the clean up, until New Year Eve, but it is said that cleaning during Tet will "sweep" the luck away. How ridiculous.
It sounds perfectly lovely. I'm afraid it is the attitude of superiority to such customs that will give the world a bland cultural uniformity.
i thought it translates literally to "Tet is come," so I put "Tet is here," but...got marked wrong. Khong chuc mung! :-(