Was it dropped? I don't think so.
The whole concept stayed similar. The significant differences (esp. appearance and things like tools) change, but that's simply due to the times changing.
The old series might look ridiculous to today's standards, but old comic versions of Batman, the Flash, etc. look ridiculous in a similar way. Some heroes got massive overhauls (e.g. Batman), others stayed the same (Spider-Man, Superman, etc.).
But even those got weird appearances on the big screen or television, e.g. watch the Spiderman movie from the 70s...
Back to Batman:
The old series was rather low budget, so there hasn't been any way to add awesome special effects or fantastic costumes (those used are still rather good for their time and they resemble the comics). E.g. the new movies depict a dark and shady Gotham, while the old series could play in pretty much any US coastal city of that time. There are significant differences, but I don't think anyone made the movies darker just because of the series being that "colorful". After all, it's still the most "accurate" comic adaption, given the available technology of the time. They added those splash screens in fighting scenes, sometimes weird camera angels similar to comics, etc. The only thing they're missing are those comic-like cuts from Hulk, but that's simply not been possible at that time.
Short version to me:
- TV series: Tried to tell stories like the comics, with costumes, abilities, tools and stories similar to comics.
- Later movies (not talking about the old/first movie): Tried to tell stories in a darker future that is believable and more serious.