Because their shareholders expect the biggest return for their money. This isn't a problem for self-funded companies (they don't have to live beyond their means if they don't need to), but if investors don't see growth they'll sell shares while it's still at its peak. That's business for you.
Yeah, the insatiable need for growth is definitely a function of the way we've structured the investment markets. Public companies depend on shareholders for capital. Shareholders buy your shares because they think you're going to be worth more money some day. Generally, companies become worth more money by increasing sales and developing new, diversified assets and product portfolios.
