As Pig stated, they weren't necessarily considered "Drab" at the time. Back then "less is more" was kind of the idea. The big problem is basically that they didn't make any effort to match existing tile. The drab tiles on the 1950's extensions are basically an offshoot of the classic IND tiles believe it or not. They evolved into that mess.
Here's the evolution cycle. They started as what we know as "IND tile" in the early 1930's:
In the late 1930's or early 1940's, the IRT did it's first wave extensions, such as was done between Grand Central and Union Square, and on one side of the stations between 14th and BB. This was actually a "glorified" IND style of tiling:
Next, that on the IND, the classic IND tile evolved into the "new IND style" that was seen in the post war IND stations such as the Fulton line east of Broadway-East New York. This is also a play on IND tiles, although more recognizable than the first wave of IRT extensions:
Finally, after Grant St, that "new style" IND tile evolved into the very clashing look that was used on the other side of the IRT extensions on lower Lex, and the upper Bway-7th Line:
Today, the "repro" tiles are correcvting the mistakes of the past. The mosaic reprodictions at so many stations are almost hard to determine whether they are real or not. And even some of those bad IRT extensions from the 50's are being covered and replaced. The below tiles at Canal are actually repro tiles. They are almost indistinguisible from the original ones in in the Canal tiles above:
