Because it can be annoying for people to go to exchange and buy your altcoin (providing that they already have Bitcoin to do it), and be subject to its volatility. But you can accept both Bitcoin and your own coin to give your customers more options, maybe even give like 5% discount for using your coin to try to boost its popularity. There are thousands of altcoins today, many of them were created as native currency for some business, and they haven't reached any major success.
Yup, fully agree, I think the altcoin markets are over saturated, and many of them turn out bad too, and end up with a few satoshis per coin. Instead of creating a new coin, why not choose a coin out of hundreds of them that is suitable for your project. It would require less work, give you and your investors more convenience if they were to buy a more popular coin than to get a new coin. Although if you create a new coin, it would be yours, but I think projects should be about innovation and using the current technologies we have today to make even better projects.
