How and who might have something to do with it but the more important reason is the rejection of parts of the Nicene Creed by Mormons. This is the key baptismal creed for most other Christians.
From https://en.wikipedia.org/wiki/Nicene_Creed
"Some sects, such as the Church of the New Jerusalem, The Church of Jesus Christ of Latter-day Saints, and the Jehovah's Witnesses explicitly reject some of the statements in the Creed, either because of a non-Trinitarian theology and/or a rejection of historically orthodox Christology."
Yup.
Most Christian churches believe that the Father, Son, and Holy Ghost are one in every way. We believe they are separate physically and have different roles, but are perfectly unified in all they do.
I think that the differences in how and who are probably closer to our reasoning behind why we don't accept other's baptisms, but I could totally understand this being why others don't accept ours.