This could be because a raised elephant trunk is considered as welcoming and showering with blessings as seen in images of Hindu God & Goddesses (particularly Goddess Laxmi). So, a straight trunk would not indicate those blessings and aplomb. In addition, elephants are supposed to signify Lord Ganesh and because of this, keeping a figurine of elephant in the house is considered most helpful and auspicious.
Also, an elephant’s trunk is considered to be a subtle indication of kundalini awareness and in this case a raised trunk would indicate a raised kundalini (where a person is receiving the blessings from such an awareness) as against of a straight trunk which would indicate a person not aware of their energy purpose in life and thus living in misery and sorrow.
Either ways, having a small figurine of these beautiful, gentle and yet elegant animals will surely add much good energy to our home decor.