For the same reason that people are still using turntables. The simple answer is because despite being “old technology,” tape is superior in some ways to digital formats, most notably for how it sounds when you have active components involved.
Like vinyl records, analog tape produces an often pleasing sound by emulating one of our ears’ natural limitations. When humans are intended to hear something, evolution has given us certain protections against things that could cause damage to our hearing. One of these is very aptly called the Fletcher-Munson curve. The idea is that our ears are most sensitive to frequencies between 2kHz and 5 kHz. This means that when something sounds “good,” it will often have a lot of content in this area because our ear wants to hear it at a higher volume than other ranges for better perception by the brain.
So what does all this mean? Well, two things really:
1) If you run an analog signal through an equalizer or anything that boosts or cuts certain bands of frequencies, you’re going to change how it sounds. This is also known as EQing, and there’s almost always a sweet spot somewhere on any given curve where the sound is most pleasing.
2) Analog equipment reacts differently than digital devices when boosting or cutting frequencies. This is because multipliers and adders work in digital devices. They’re essentially adding or subtracting decimals, which means you never have the exact numbers on both sides. This is fine if you want to get back to where you started, but it’s pretty important if your goal is to produce a pleasing sound for humans. Because of this, digital equalizers are only designed for making something more rigid/flat, not better sounding.
You can use digital eqs for this, but it’s often not the best method.
Never fear, though! We have tape decks which you can boost and cut frequencies as if their lives depended on it. Some of the mastering engineers who used to be able to work with vinyl still prefer working on a properly maintained analog deck because they can get a more pleasing sound even at low volumes than what they could with something like Ableton Live on a computer which is better for making sure that things stay on point. So why wouldn’t everyone want an analog mixer? Because they’re expensive as hell and take a lot of maintenance if you want them to last longer than a few years. This brings us back around to tape decks, or more specifically, Multi-Track Tape Decks.
Well, they have more than one tape head to record more than once on each side of a tape. This means that if you want to do some serious recording and get the best sound possible, you use multi-track decks and run things through EQs and compressors, just like an analog mixer would be used in the studio. For home studio folks, this is even better because it’s often easier to find cheap “prosumer” or consumer multi-track decks instead of finding pro-level analog mixers for cheap.