Zoho has never had the policy of spending other people’s money, just its own.
Zoho has been around since 1996. They’ve already invested the time and resources into developing these apps. It doesn’t cost them much (server time, customer support, developers) to maintain and improve the software.
Most companies that have such a robust product suite are publicly-traded on the stock market: shareholders and Wall Street howl at them to increase revenue and profits and shine a spotlight on them every quarter.
Zoho, on the other hand, is privately-held and profitable — they have no impetus to grow at a certain rate or maintain a certain profitability level.
Zoho is an Indian-American company — HQ and several sizeable offices are in America, but much of their developers and support staff are in India, where employee compensation is lower than in America. Don’t let this fool you into thinking that their products aren’t high-quality.