Because every good business needs a good website.
A good website is a good employee.
Just like a good employee, a good website should be able to tell a potential customer: what your business does, how it does it, what it can offer the customer, and maybe even be able to offer some services to the customer itself.
A good website is a presentable employee.
Just like a good employee, a good website looks intentional and professional. When someone is looking at your website you would not want them to think it looks slapdash or gaudy. It should be easy for someone to understand what the point of your site is and how they can use it.
A good website is an organized employee.
Just like a good employee, a good website has all its information labeled and organized. When a potential customer has a question about your business, or a need for a web application you offer, it should be easy for them to find.
Because first impressions are important.
Everyone will tell you the same thing, first impressions matter quite a bit. They are what people use as a frame of reference for when they interact with you in the future, or to decide if they even want to communicate with you again at all. We live in an information age; if someone wants to know something the will look it up, so if they want to know about a business they'll go to their website. Since your business's website is likely the first thing a customer is going to see it is important that your website leaves a good first impression.
Because convenience is important.
Getting people to use your website beyond just establishing an idea of who you are means it should be convenient to use. No one wants to navigate a rats maze of links just to find one thing. The information on your site should be organized and easy to find, and the same applies to any tools available on your website which should also be easy to install/use.