Over the last two decades (at least) whenever Republicans have had the opportunity they have cut the operating budget of the IRS. This elicits cheers from a lot of people; I mean, who likes to pay taxes? But the IRS doesn't make the rules, Congress, abetted by the President, makes the rules. And those rules, despite regular pledges by people running for office to simplify the rules, just get more convoluted and Byzantine all the time. And the IRS has fewer and fewer resources to keep track of all the rules and to be able to track down those who avoid their legally due tax bill.
Something you'll hear from time to time is that it's the ultra-rich who are the ones who are sliding out from under their full tax burden, while it's the lower income people who get hit with interest and penalties. Part of the problem is that for lower to middle income people the ways to avoid taxes are few and straightforward. Someone gets a second job and is paid off the books, or takes an occasional cash gig. About twenty years ago I was delivering newspapers in the early morning and didn't report the income. The newspaper, however, sent copies of the 1099 to the IRS and I got caught. The interest and penalties added up to close to half of the added gross income that I had earned at that second job since this extra money was added on to what I was already earning at my regular job. I didn't have a leg to stand on since it was without question taxable income. Someone who has earnings in the millions or billions has more tax avoidance options than simply not reporting income from a second job, and those options are usually more complex.
One popular way for the super wealthy to avoid taxes is to have access without actual earnings. Billionaires routinely finance their lifestyles by taking out loans with their stock holdings as collateral. Since unrealized stock gains are not taxable until the stock is actually sold, they are living off loan proceeds, which are paid back with the profits from appreciated stock value (that's taxed, but a small portion of what they're living off). The very rich often own a web of interlocking limited liability companies (LLCs) which, if you have a smart accountant, can have a paper loss. LLCs are what's known as "flow-through entities", whereby the profit or loss "flows through" to the owners. The loss is often borrowed money anyway, but the loss that flows through reduces the owner's tax bill. Then there's deductions and credits for various reasons that may or not be legitimate, but with not enough staff to sift through it all, and definitely not enough staff competent enough to decipher the complicated accounting, the billionaires are rolling the dice that they won't get caught. So, not only do the Daddy Warbuckses of the world have more options to shelter their wealth from taxation, they are less likely to get caught when they cheat.
One thing that gets reported as sort of a scam, but really isn't, is depreciation. In a business, taxes are paid on the profit, which is gross revenue minus expenses. With large asset purchases, however, business are required to spread that expense over the useful life of the asset. The useful life varies from 39 years for buildings, down to 5 years for laptop computers. The simplest type of depreciation splits the expense into equal amounts over the life of the asset. It's not a way to get out of paying taxes, and it doesn't equate to getting your asset for free, it's just a way to spread out the tax benefit of a large purchase.
Part of the recent large bill passed by the Senate Democrats was to increase the IRS budget by $80 billion over 10 years. The Republicans are screaming that this will mean 87,000 new auditors who will target middle income Americans and small businesses. While the 87,000 number of employees is mentioned in a recent Treasury Department report, the increased budget will not only go toward hiring, which will include not only auditors and other enforcement agents, but IT and customer service positions, and also toward technology upgrades, which are sorely needed and it's slated to be spread over 10 years, when around half the current 72,000 IRS employees will be eligible to retire.
The IRS is not the problem. They are merely the agency tasked with carrying out the laws that Congress has passed and the President has signed.