(So my blog stats tell me that either someone in the Philippines has been methodically reading through every post on my blog or a whole bunch of people there have been reading it. Either way, hello!)
Most often, if "Mara" is mentioned in a mythological or religious context, it is not a goddess being discussed at all, but the Buddhist demon Mara. This Mara is best known for being the essence of the temptations if the physical world.
As Sidhartha sat beneath the Bodhi tree and approached enlightenment, it was Mara who tempted him with riches, with comfort, with his lovely daughters. Does it seem disrespectful to compare this demon to the goddess I work with? And yet the goddess Māra does rule over the earthly world.
The Buddha acknowledges that all of the things in her purview are temporary and illusory pleasures: the crops, the marketplace, the body. For someone who believes that desire leads to suffering, then of course you would see the goddess of all earthly abundance, and the body after death, as a distraction your path. Mara is therefore characterized as a demon because what she rules is what followers are told to avoid.
I want to make clear that I don't think the Buddha or his followers actively demonized the goddess Māra, or that she actively sought to tempt him. Plenty of Buddhists don't even believe in demons or gods. Time, distance and the development of Hinduism from Vedism stand between the separation of the proto-Baltic people from the Indo-Iranians. Rather, I think the concept or archetype of a being in charge of worldly abundance is a common root between the two.