1. they're not competing, they're doing different jobs
Instagram is brilliant at reminding people you exist. It's built for people who already follow you, scrolling past your latest post between everything else in their feed. A website is built for people who don't know you yet and are actively searching for what you sell. Confusing the two is where things go wrong.
2. the search problem
Search "plumber Crouch End" or "salt beef bagel Muswell Hill" on Google and Instagram profiles rarely show up in the main results. A website, properly set up with your services, location and the right words on the page, has a real shot at ranking for exactly those searches. Without one, you're invisible to anyone who hasn't already heard of you and gone looking for your handle specifically.
3. the algorithm problem
Instagram decides who sees your posts, not you. Organic reach on business accounts has fallen for years, and it's common for a post to reach only a small slice of your followers unless you pay to boost it. Every post you make is effectively rented space. A website is the one channel where you're not competing with an algorithm for your own audience's attention.
4. the first impression problem
47% of people form a judgement about a business based on its website design, and 84% see a website as more credible than a social profile on its own. When someone's comparing you to two or three competitors, the one with a proper site, real photos, clear info, a way to get in touch, wins the benefit of the doubt more often. A grid of nice photos on Instagram doesn't answer "are these people legit" the same way a website does.
5. the ownership problem
Instagram can restrict, suspend or lock an account, sometimes with no warning and very little recourse. If that's your only online presence, your entire digital footprint disappears with it. A website is the one asset in your online presence that's actually yours: your domain, your content, your rules.
6. what good actually looks like
The businesses getting the most out of both aren't choosing one over the other, they're using Instagram for personality, behind-the-scenes and staying visible to existing customers, and a website for search visibility, credibility and turning "never heard of you" into a booking or a visit. Neither replaces the other. Instagram brings people back. A website brings new people in.
7. the real cost of instagram-only
It's rarely dramatic, it's a slow leak: a few searches a week that end at a competitor with a site, a few people who assumed you'd closed down because they couldn't find anything beyond a profile, a few who just went with the business that looked more established. None of it shows up as an obvious loss, which is exactly why it's easy to ignore.