The long-run rise in the net capital income share is mainly due to the housing sector-it is not entrepreneurs and venture capitalists that are taking an increasing share of the economy, but land owners

See Piketty, Housing, and Capital Share from Alex Tabarrok.

"Gianni La Cava has a very interesting article (based on a longer paper) on what accounts for the rising share of capital in the income accounts:

A key observation in Thomas Piketty’s Capital in the Twenty-First Century (Piketty 2014) is that the share of aggregate income accruing to capital in the US has been rising steadily in recent decades. The growing disparity between the income going to wage earners and capital owners has led to calls for government intervention. But for such interventions to be effective, it is important to ask who the capital owners are.
Recent research has shown that the long-run rise in the net capital income share is mainly due to the housing sector (e.g. Rognlie 2015, Torrini 2016 – see Figure 1). This phenomenon is not specific to the US but has been evident in almost every advanced economy. This suggests that it is not entrepreneurs and venture capitalists that are taking an increasing share of the economy, but land owners.
…The decomposition of the national accounts by type of housing indicates that the secular rise is mainly due to a rising share of imputed rent going to owner-occupiers. The owner-occupier share of aggregate income has risen from just under 2% in 1950 to close to 5% in 2014 (top panel of Figure 2). The share of income going to landlords (i.e. market rent) has also doubled in the post-war era. But, in aggregate, the effect of imputed rent is larger simply because there are nearly twice as many home owners as renters in the US economy. A similar phenomenon is observed in the personal consumption expenditure data (bottom panel of Figure 2). In other words, today’s landed gentry are predominantly home owners, not private landlords.
…The geographic decomposition reveals that the long-run rise in the housing capital income share is fully concentrated in states that face housing supply constraints. To see this, I divide the states into ‘elastic’ and ‘inelastic’ groups based on whether the state is above or below the median housing supply elasticity index (as measured by Saiz 2010). This index captures both geographical and regulatory constraints on home building across different US regions. For 50 years, the share of total housing capital income going to the supply-elastic states has been unchanged at about 3% of GDP (Figure 3). In contrast, the share going to the supply-inelastic states has risen from around 5% in the 1960s to 7% of GDP more recently. Notably, these divergent trends in housing capital income are not due to a few ‘outlier’ states where housing supply is particularly constrained, such as New York or California – instead, there is a clear negative correlation between the long-run growth in housing capital income and the extent to which housing supply is constrained across all states (Figure 4)."