SteamVR opens when you play Roblox because of a glitch in how Roblox works with SteamVR. This problem makes SteamVR start automatically when you launch Roblox, even if VR settings are off. It has been reported many times and has been fixed, only to come back after updates.
Many users have experienced this issue and have looked for solutions. Some temporary fixes include renaming the SteamVR folder or editing the Roblox settings file. These methods can stop SteamVR from launching with Roblox, but they are not permanent solutions.
The issue keeps coming back because Roblox updates sometimes reintroduce the problem. This makes it frustrating for players who do not use VR and want a smooth gaming experience. The Roblox team has worked on this, but a consistent fix has not been established.
For now, players can use the temporary fixes to avoid SteamVR from opening. Regular updates from Roblox may eventually solve the issue for good, but keep an eye on forums and community discussions for the latest workarounds.