We assume that Core PHP means solving a Mathematical problem by using paper and pen. Frame work means solving Mathematical problem by using a calculator.
Only some students can achieve results by using paper and pen as same as in PHP. Only a few of the developers can write the code in an easy way and reliable format.
Everyone can achieve the result by using the calculator as same as in PHP. Even beginners can write the code in easy way and reliable format.
The main problem with core PHP is when developers write own logic, it is difficult to make it out for the result so most of the developers are choosing innovative frameworks.
Most of the frameworks are reliability, consistence and time saver. Some of the innovative frameworks are having the rich set of functionalities, so developer no need to write whole code, Developers needs to access the code by using framework and develop a PHP web application. Frameworks don't give the solutions for bad code writers, but it gives reliability while writing code.
Everyone wants to move into sophisticated technologies. If any website or web applications have developed in Core PHP, it is difficult to enhance the website components, but if website or web applications has developed in Frame Work PHP, it is very easy to enhance the features.
It's not at all bad. Core PHP helps you write the code and understand the code. when the developer at begin stage, we strongly recommended to learn Core PHP, cause we don't want to see you as a bad developer. According to World theory, easy always gives best result with strong base. As per the world theory, if you know core PHP, you would reach your goal by using framework PHP.