In the novel 猫城记, why does 老舍 use 的 (instead of 地) for adverbs?
Actually, you're right, this is a history question rather a grammar one.
Chinese people do NOT differentiate &quot;的得地&quot; intentionally before the 1960s (or even 1980s).
Here is a blog I found “的地得”的历史——《得的篇》（上）, saying 老舍 mended his &quot;的地得&quot; in his new publications after 1956.

1956年，教育部颁布了一个叫《暂拟汉语教学语法系统》的文件
里面规定：“结构助词包括: 的、地、得、所。它们是定语、状语、补语的标志……”
...
一个证据是，上面用“马马虎虎的铺好”的老舍先生，在1956年以后出版的作品修正了对的地得的用法。

Another one I found is &quot;的地&quot; could be the same from “的地得”并未通用, suggesting that &quot;的地&quot; could be written as &quot;的&quot; at that time.

1984年人民教育出版社中学语文室编印的《中学教学语法系统提要(试用)》提倡“的、地”合写为“的”

So why &quot;老舍 use 的&quot;?

猫城记 was published in 1933, when &quot;的得地&quot; are not clearly defined at that time.
Even if the book was re-edited and republished, &quot;的、地&quot; could be the same.

Well, those links are not official resources, but that could be &quot;八九不离十&quot;.
In my opinion, do not bother grammar mistakes for those classic publications anyway.
Just like people don't learn English grammar by reading Shakespear.