A common response from students is “Why are we learning this? DreamWeaver will do it for me. I can always look it up when I have work.” Oddly, I never hear that from anyone actually working in the industry.
To understand my point, allow me to reframe the question:
“Why should I learn French if I’m going to live in France? Everything I need is in a dictionary.”
“Why should I learn how to weld a gas pipe? If my boss asks me to do it, I’ll just look it up then.”
HTML and CSS are languages: perhaps not in the classical sense or within computer science, but they are languages all the same. DreamWeaver does not tell you how to create a web site any more than a French dictionary teaches you to speak French. A degree of fluency is required in the language before either tool approaches utility.
The truth is, a web developer will always be learning on the job, as new technologies and techniques come in thick and furious. References are just that: a means of occasionally jogging memory. Dependence on such a tool would be like flipping up a pair of goggles to read “Welding For Dummies” while holding an acetylene flame in the other hand… as live gas flows through an open pipe.