Firstly there are significant barriers technical to access - proving ID and no bulk access. So analysis of the data is hard to start with.
But most importantly, the lack of open licence means you can't share the data with others, publish cleaned-up data, publish comparisons or linkage with other datasets or publish derived data. You can't crowd-source any aspect of the data process. You are on dodgy legal ground if you publish visualizations of the data (its derived). Can you afford a lawyer? About all you can publish are summary stats. Newspapers, academics and campaigners might doubt it is worth this huge effort to overcome the barriers to do the analysis and publish only those summary stats, because it is so hard for others to reproduce the work for validation.
What CAN you do with it? Someone can manually check who owns a particular plot. Which is an age-old use case. Making it free instead of charging a small fee changes little.
The lack of open licence makes it clearly non-open, according to the open definition. And the allowance for citizens to view one-off records does little to support the aims of open data.