Zoroastrians Dwindling in Iran

Since the islamic revolution in Iran, the Zoroastrian population has shrunk in half to 45 000. Many have emigrated to the west for job opportunities and a better life. A Zoroastrian MP insists the exodus of Zoroastrians out of Iran is not due to discrimination. But at the end of the article he adds this tidbit:

But Niknam also said there were problems with Iranian legislation under which a member of a minority religion who converts to Islam gets all the family inheritance.

"What do you think will happen to the family? It will be undermined," he said. Niknam said he had petitioned Khomeini's successor, Supreme Leader Ayatollah Ali Khamenei, about the issue and suggested he was hopeful for a change of the rules.

Why is that? Could it have something to do with the ideology of islamic supremacism? I'm sure there are a lot more reasons why the Zoroastrians are moving out of Iran.