Your website looks and feels outdated.
Yes, design paradigms are changing faster than ever, and the potential leads who are browsing your website will not have a good impression of your business. Even if you are a rocket scientist, a bad website would not get you any new customers – check https://www.spacex.com/ (just taking the rocket scientist analogy to the next level) which is actually built using a CMS called Drupal.
Google Analytics provides you with free traffic monitoring and is the de facto standard for small, medium or big companies. If you see a reduction in traffic and the trend continues, then it is time for you revamp your site. In case your bounce rate is high then it means that either the User Experience of the website is not good, or the content lacks value. You can actually type in your questions in Google Analytics to get answers –
How and why would anyone visit your website? It could be either that you are running certain ads, there are some keywords in your content/website that help drive traffic organically (of course off page SEO would play a big role in this), or you are a big brand so people are directly searching for you. In all these cases if the user does not derive any value from your content then they will leave, and you will lose the trust of the lead/customer. Your content needs to be relevant, fresh, unique, optimized and most importantly up to date. Your choice of keywords must be well thought out, and strategically implemented on the website. In addition, on-page SEO should be done for the website.
The best way to learn that your website is being found but lacks content is when you have high number of entrances and a very high bounce rate, with a low period of time spent on website. That is the typical symptom of a website that needs a content overhaul.
The above example shows analytics of a website that has good content.
Page loading takes eternity
Does not work properly on mobile
This means your website is not responsive or mobile friendly. In today’s time, this could be the death of your website as such properties are penalized by Google and other search engines. Your website should behave according to the device that is being used to open it. There are certain frameworks like WordPress that have themes which are responsive by nature. Even if you are building a custom website then the CSS (cascading style sheets) need to be updated for the responsive design.