Historically, knowledge-workers had little interest in unionizing because they knew they possessed the ability to learn and adapt. Sure, they had useful skills and knowledge. But much of I.T. is about possessing the ability to learn new things quickly. Everything's in constant change or evolution. The software package you use today will get a new update in a matter of weeks and then it has new functions or features have been moved around to new locations in it. The programming language you use may even get deprecated, demanding you learn whatever replaces it. The hardware you troubleshoot and support changes on a regular schedule.
Unions primarily benefit people who want to retain fair compensation for doing the same specific tasks repeatedly. They want reassurance they won't be forced to do anything new that's outside the scope of what they were hired for. Such a thing requires a new job title/role and a contract specifying exactly what they agree to as part of it.
I.T. workers usually felt if they were getting a bad deal someplace, the best move was to quit and find a new job where pay/benefits and/or working conditions were better. There wasn't so much fear or concern if a place used different software or tools than what they used before. That didn't matter much as long as they could learn the differences between it and what they had previously.
I think that might be changing in recent years, though? Now, you probably have an edge if your resume shows you already worked at companies people are familiar with and impressed by. But otherwise, they mostly want newer/younger people who they can pay lower wages to and get the most out of. Most places are starting to treat anyone in I.T. as more of a necessary expense than an asset to the business, and fewer and fewer pay well for your decades of experience.