Explain the high-level reasons that are responsible for the development of selenium tools from Selenium RC to Selenium WebDriver?

The problem with Selenium RC was that its interaction with the browsers was not realistic, it used a JavaScript interface to interact with the browsers. This indirect interaction with the browser affected the performance of Selenium RC.

Selenium WebDriver in fact inherited almost all the features of Selenium RC be its Language support, OS support or cross-browser support. This was the reason that they decided to merge Selenium RC with Selenium WebDriver. The only thing Selenium WebDriver added to Selenium RC is, it ensured that WebDriver interacted directly with the browser, making the interaction more realistic and thereby improving its performance.