If I buy $10k of Intel, it grows to $15k and I sell it to buy $15k of Google, I owe tax on the $5k gain.
Now, perhaps one could argue that there is no “liquidity” event by trading one crypto for another. But perhaps the IRS argues there is a phantom liquidity event during such a trade. The IRS generally doesn’t like someone to be able to trade assets without recognizing a gain, otherwise it breaks down the fundamental framework upon which the entire tax system is based. The law provides a few provisions for tax free trades, but they are specifically prescribed by the tax law, such as a 1031 exchange between real estate holdings.
If you’ve heavily traded between cryptos over the past year with massively appreciating values, I would be worried that the IRS would claim you should have recognized a tax gain with every trade. For some, the ramifications for such a perspective could be huge.