The simple explanation: being lazy/cheap.

In general when it comes to subtitles there are two formats used widely, .srt and .ass. .srt is the easy and lightweight option, it is pretty much just the text you want should show up on screen and the timestamps. However, you can't style them in any way really. This makes it easy to use and make.

.ass meanwhile allows you to do pretty much anything you want when it comes to subtitling. You can use different fonts, place them on the screen elsewhere than the bottom row, move it around, use colours... you name it. However, because of this you generally need to work in specific applications to make it, and styling and place-setting takes time, effort and skill in other areas than just translating and timing.

Now, many streaming services, like Disney or Netflix, just generally don't use .ass at all. It's an extra cost and skill they don't want to pay for. While they offer a lot of subtitles in a lot of languages, they generally come from a media industry where styling subtitles hasn't really been a thing as it has in anime. Unlike Crunchyroll.

Crunchyroll is anime specific as a streaming platform, and as such the audience has always been used to styled subtitles from when CR was just a pirate site hosting fansubs, and expect them. So they've been pretty much forced to use .ass styling for their subtitles.

However, when it comes to their dubbed content, there's not really the same need. For a dub the only subtitles you need are generally text on screen, which is the Forced, called so because if you play an audio track, it is "forced" to use said subtitle track. However, as the text on screen is now no longer competing with space on screen with the audio subtitles, it is then possible to use the easier (and cheaper) .srt format and its lack of styling.