That is the main point. They already have applications which they can check for features, also they are open-source. They are not inventing the wheel, they only needed to implement same or better features which are already available for a long time in the market.
Also, getting more funding doesn’t mean that they can do better. Proton already has 400ish employees and over 100 million accounts (Ref), and they are giving away millions of USD to charities and organizations every year. So, money is not the issue here.