At some point or another when browsing the internet, a site will come up that makes you want to stand on the top of Mount Everest and shout "What idiot designed that site?"
But that statement isn't always fair. There are a lot of reasons why bad websites get made.
The ever-changing world of technology can wreak havoc on a websites potential. A site built five years ago isn't going to look the same in today's browsers. Not to mention a site being mobile responsive. And what if your site is on a content management system like Drupal or Wordpress. Has the site been updated with the most current version? Too often, the limitations of the technology being used to manage a website mean that problems remain unresolved and improvements cannot be made without an investment of money and effort.
The goals of an organization are not always aligned with those of its customers. In a perfect world, businesses expect you to sign up for newsletters, view ads, and provide contact information simply because they're asking you to. What the user wants is to complete whatever it is that brought them to your site and then leave.
This can lead to website design decisions that organizations THINK will help them (pop-up forms, ads that block what you're trying to read as you scroll, etc.). They think any attention is good attention, but for a website that isn't always the case.
More often than not, a company is their own worst enemy when it comes to website design. These types of projects are a constant struggle against what a web designer/developer (the experts) know to be true and what your second cousin's son's step-uncle that once built a website in 1999 thinks a modern website should look like. Be weary of taking Uncle Bob's advice, even if he is telling you what you want to hear.
A good website design company will take your objectives, goals, and their research of your customers and turn it into a great website. It won't always look like what you think it will.
Great websites are considered a success if the visitor knows within 10 seconds what they're supposed to do. The fancy term marketers use is "Call to Action." Don't let your homepage get bogged down with too much information. Focus on the goal of your customer or potential customer. Do you want your visitor to register for an event? Download your white paper? Contact you? Make those actions as clear and easy as possible.
One of the biggest reasons poor design decisions are made is because organizations have too much work on their plates to focus on making customer and goal-oriented decisions about the site design. They tell their web developer they want a website just like their Uncle Bob described and aren't able to take the time to learn what their website SHOULD look like.
Never discount the importance of the Highest Paid Person's Opinion (HIPPO). It's not uncommon for the web team to arrive at a design direction or decision, only for it to be overruled by the head marketing honcho or exec.
Few stakeholders will pay much attention to content or support of user goals, instead focusing on the overall visual design, branding, color scheme, and so on. If some or more of those elements don't match their personal preferences, it's back to the drawing board, regardless of how well the design functions from a user standpoint and whether it supports the site's overall objective.
Everyone's interpretation of what is 'good design' and 'bad design' doesn't matter. What matters is if the website meets your customers or potential customers goals. If the site is generating leads and delighting customers, it's a successful site.