The more you know about your ecommerce customers, the better you'll be able to create value for them in your products and your marketing. The more value you create for your customers, the more value they'll create for your ecommerce business through purchases. So collecting customer data is a win-win—you carry better products and have better targeting for your marketing, they get better solutions to their problems.
You already know how valuable an engaged audience can be. You build sales funnels because you know that getting someone to sign up for your email list or click on a social media post makes them that much more likely to buy. You know that businesses have a 60-70% chance of selling to existing customers, as opposed to just 5-20% for new prospects.