Unless you don't copy the license terms, it's impossible to "steal" open-source code. That's... sort of the point.
Many open source licenses levy restrictions upon the acceptable use of the software. Those restrictions may include attribution requirements, up to and including a requirement to include the license when redistributing the code; they may forbid using derivative works for commercial purposes; they may require the downstream project to utilize the same license. Open source is not the same thing as "anybody can do anything they want forever."
Unless you don't copy the license terms, it's impossible to "steal" open-source code. That's... sort of the point.
Copyleft is still a thing. Right to attribution is still a thing. Please, read about it and you will discover that there is a lot of nuance to the open-source code.