The main reason is that your company garners a strong, positive, reputation. Since reputation is everything in business, doing anything to tarnish it will see your revenue plummet. A strong reputation allows you to build trust and relationships with suppliers, business partners, employees, and customers. It also allows your company to grow at a faster rate.
The quality of your products and services are better when you act with integrity. It ensures you act swiftly and appropriately to fix a problem should any arise. And as a sign of goodwill you'll compensate your customers with small gifts as a sign of your sincerest apologies for the inconvenience caused.
Leading with integrity paves the way for your employees. They know what is expected of them and what is not tolerated. It promotes good company culture. Setting a good example allows your employees to make good decisions and build on the relationship you have with customers. They'll be able to trust you and your actions knowing that everything you do is rooted in good values that don't go against their own core values.
Ultimately, you're trying to keep your business alive forever (if you can). Having integrity in your business helps you achieve long-term success. Doing what's right will have you facing problems upfront but reap the benefit in the long run. Focusing on integrity allows you to focus on winning the hearts of many and getting the best long-term results.
There is no good reason to opt out of choosing integrity in your business. The benefits outweigh the disadvantage (if any).
Build a strong positive reputation
Produce better quality services and products
Promotes good company culture
Helps long-term success