Answer:
Basically foreign firms trade ADR's in Nasdaq, NYSE or other OTCs because they want to access more investors.
To be honest, trading an ADR makes more sense for the Indian Company since the Indian capital market is not that large and investors are scarce. Maybe the Indian company cannot get any more money from its capital market. For the Indian company it is clearly a very advantageous opportunity.
Understanding the motivations of the Japanese company is more complex since Japan has a large capital market and its savings rate (= investment rate) is extremely high, so there is a lot of money available for investing in corporations. Listing ADRs is generally more expensive than listing normal stocks since you must have a depository institution that charges a fee in addition to other normal expenses. The only reason I can think of why the Japanese company wants to list ADRs is that they are trying to invest in the US and they would prefer to obtain "local" funding for these specific investments.
