The tax laws are vastly more complex than GDPR. The maximum penalties for tax fraud seem to be $250,000 + cost of prosecution + 5 years in jail.
If you make a small mistake on your taxes, and the IRS notices, you will probably receive a warning and have to repay it with interest. If you make a negligent mistake, you may be in addition be fined a small percentage, like 10-20%, of the amount you failed to declare. You have to conduct very large scale and intentional tax evasion for the maximum penalties to apply.
The IRS could argue for and try to apply the maximum penalties for a lemonade stand, but they don't. And people go on with their lives, put in their best effort to comply, and can be confident that they will be treated fairly.