Nitro has many useful advantages for people who spend a lot of time in Discord like the ability to upload larger files, send longer messages and customize your profile, but I’d say you don’t have to be an expert user to appreciate aesthetic changes. It’s easy to imagine people wanting themes but not being able to justify such a high price tag for an app they’re just casually using.
Discord lets you preview the themes to see what you could make the app look like if you goods a subscriber. (You can open the preview pane by going to Settings > Appearance and then clicking the “Preview Theme” button.) In my opinion, there’s a nice mix of pastel light themes and cool/moody dark themes – there’s even a “blurple ” ” one that almost feels like one Forget theme.
For people who don’t want to pay for Nitro, there are still ways to theme Discord. The BetterDiscord project has been working on improving the app for a while and the list of improvements includes a theme engine. And while it really does let you create custom themes rather than giving you a ton of ready-made themes to choose from, it’s admittedly not quite as user-friendly as the Nitro version.