Because you'll be taxed on something that often has no liquidity nor market. The estimated value on your stock may be $5 and you'll get taxed on that but if you

Because you'll be taxed on something that often has no liquidity nor market. The estimated value on your stock may be $5 and you'll get taxed on that but if you were to go sell it you may only be able to fetch a fraction of that on the secondary market (if there is even one for those stocks), possibly not even covering the taxes you have to pay.