WordPress, Joomla and other Content Management Systems (CMS) are an easy way for somebody to start a Website as they are easy to update via their Password Protected Admin Backend. (For most cases NO FTP Uploads and editing of Files required.)
But don’t rule out some really nice HTML Templates or Themes.
Some Reasons to choose HTML

• Total control over your SEO. Nothing in the programming world exist like HTML for controlling elements. A website in HTML is essentially made 0f brick and mortar. Unlimited customization ability. WordPress doesn’t even come close.
  For example: In WordPress one will have to be at the mercy of developer to change factors like reducing https requests or will have to do it by him/herself, which most probably will end in a crash for less experienced people. And the work involved will be restyling the entire styling components, which is a time consuming job that I wouldn’t recommend.
• Some of the plug-ins in WordPress help in reducing HTTP requests, browser caching, cache expiry etc. and it is easy to get a good score in tools like GTMetrix, Page-speed etc. However in real life situation these websites can be real slow, which will make customers bored. The scores in such tools depends more than just page loading time. For example, a website loading in 5–7 seconds also can fetch a score of 90+. But the question remains the same- Will customers wait till that?. And the plug-ins misses many of the portions that can be optimized. If you plan well in HTML, these mistakes can be easily avoided.
• You can customize website any way you want. WordPress have limitations in this. You will have to have a child theme built for this purpose. Although I would suggest to avoid HTML for ever updating websites.
• Build adaptive websites. If you choose WordPress it is quite difficult to spot an adaptive theme. The chances are slim to none. Adapt to any mobile screen and no issue of “Size target tap” for user experience. Mobile friendliness matters for some search engines.
• HTML and CSS can be easily understood by search engines. In WordPress if you use the plugins and dynamic components. It might not be a suitable option for SEO.
• No worry of updated versions. WordPress constantly update versions, which requires updated plugins also. If the plugins are not compatible, you are forced to find an alternative plugin that does the job. Changing the appearance and may be resulting in performance issues and SEO problems.
• Since you know the web structure easily, the sitemap will have a simple index which is recommended by all the search engines. You can also specify the frequency in which the contents are modified so that crawlers can come and do their job at the same time frame. Advantage in SEO.
• Faster in operation : For most basic websites with less dynamic contents HTML will usually outperform WordPress. Loading time matters in SEO.
• WordPress themes’s junk problem. The amount of non-utilized codes will eventually slow down the entire website. Even using cache plugins will not do much help, if the redundant code is dynamic in nature.
• Even a slight error in back end coding can shut down entire website. HTML doesn’t. Search engines uses up/ down time in their metric.
• PHP can be easily aligned with html and used for dynamic environments and bring the functionality that WordPress offers.
• HTML websites will offer more security as WordPress is a common platform as such. Any vulnerability reported is applicable to most websites running on WordPress. Hacked websites lose ranking in Google.
• If you are an expert, editing will be more simple in HTML, It is a bit difficult to understand the structure of WordPress. Not related to SEO but still a valid point I guess.