Am I guilty of a self-written engine?

Question

CMS

Hello, can you tell me what my fault is and whether I made a gross mistake?
I myself am a 2nd year student studying programming and web development. As a pumping front-end and back-end skills, I decided to take an order for freelance. They asked to make a site, seemingly standard, article pages and a form submission page.
Well, I’m looking at their old site on joomla, they didn’t even update it and didn’t add content. With joomla and WordPress, I worked at the content manager level. Therefore, somehow I didn’t want to start with a free engine, I wanted to make a light version of the admin panel and site management.
Thus, I came to the conclusion to write my northern architecture. Own engine that implements simple actions, adding pages, editing, module: sending and editing reviews. I wrote a minimal template engine to work with a template and embed content based on a site page. I shot a video on management and provided it to the customer. It took 3 weeks for everything (design and backend from scratch). I took 12 thousand rubles for this (students want to eat, but rather it was greed and ignorance of the prices of sites).
Here is a video, site management: www.youtube.com/watch?v=hzKwDynAetc
A month later, a customer writes to me, allegedly he hired a SEO specialist, and he said that all sites should be on WordPress and poured dirt on me that I was a thief and a deceiver. I felt ashamed. They ordered a transfer to wordpress from someone and now I'm blacklisted on their phone.
Tell me what I did wrong as a novice coder? I just wanted the best, to learn something, to do my own, but at the same time earn some money (for motivation). Is it worth taking the time to write, promote, improve your engine, or do you need to be exclusively a wordpress developer. Wordpress is a popular and good system, but there are other systems, it’s not so easy to create them, and you want something easy and understandable in terms of code architecture in order to understand the whole php kitchen. But maybe I'm wrong and chose the wrong path and all deceit, university, profession. You can be very driven about this if at the initial stage of your formation you will not be appreciated and you will make gross mistakes all the time.

Answer 1

on the one hand, the SEO nickname is wrong, because .. well, this is a very stupid statement.
On the other hand, you were wrong exactly when you decided for fun (to satisfy your desire for self-development) to write everything from scratch. Okay, there is a CMS, but writing your own template engine as part of a commercial project is already too much. Experiment for health but not within the framework of projects for money. This can only be afforded by people who have worked with existing systems for a couple of years, and these very existing systems are already squeezing and hindering them in order to perform some tasks.
That is, the claim of the SEO-nickname may have been due to the fact that:
- there is no sitemap and no means for generating, and since this is not WordPress, simply installing the plugin will not work
- perhaps there is no way to set all this SEO crap like meta information, etc.
- all in such spirit. Any "finishing" to the client will now cost a substantial amount.
Moral: experiment in your free time, gain experience. Try to use ready-made solutions. In addition to wordpress, there are a lot of small and convenient CMS with basic things that SEO specialists need and are easy for programmers to finish.