There are a few things:

1. There is an entire network of computers in modern cars, monitoring everything from air/fuel mixture to tire pressure. Automotive engineers have far more data to play with than those from past decades.
2. Those computers and the network they’re connected to are significantly more powerful than in past decades.
3. Direct injection has gone from a novelty to a mature technology. Combined with optimized intakes, and an increase in the number of O2 sensors + some fine tuning of where they’re located, it’s much easier to dial in the perfect air/fuel ratio.
4. Direct ignition and some very advanced variable valve timing make ignition timing super accurate. That lets cars change ignition timing on the fly, which can really boost power down low & up high in the rev range.
5. Modern metallurgy + all the other changes have allowed for much higher compression ratios without risking detonation.
6. As others have mentioned, turbos! Modern turbos produce power over a much wider rev range & tend to be tuned to produce peak power lower in the rev range, making the car feel faster in daily driving scenarios.

I’m an old school gearhead and will always miss the cars of old, but modern cars are truly a marvel. We’ve taken something that is smokey, oily, and a gross polluter and turned it into something that’s hard to smell even when you stick your face near the exhaust*.

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* I don’t recommend trying this