That is probably because of IRC §164(b)(6):
(6) Limitation on individual deductions for taxable years 2018 through 2025
In the case of an individual and a taxable year beginning after December 31, 2017, and before January 1, 2026—
....
(B) the aggregate amount of taxes taken into account under paragraphs (1), (2), and (3) of subsection (a) and paragraph (5) of this subsection for any taxable year shall not exceed $10,000 ($5,000 in the case of a married individual filing a separate return).
The preceding sentence shall not apply to any foreign taxes described in subsection (a)(3) or to any taxes described in paragraph (1) and (2) of subsection (a) which are paid or accrued in carrying on a trade or business or an activity described in section 212.
So, the issue is whether or not holding vacant land as an investment is a Section 212 activity and there are divergent opinions on that. If you believe it is, and want to take the deduction, then it is probably best to enter it on Line 6 of Schedule A. With respect to the position of the IRS, do not be surprised if they disagree with your position.
