Am I missing something here? The report goes to say it will cost $1.1 trillion more over the period sanders estimates... But doesn't explain why. See the exerpt:

Results

The plan is underfinanced by an average of nearly $1.1 trillion per year. TheSanders campaign estimates the average annual financing of the plan at $1.377 trillionper year between 2017 and 2026. Over the same time period, we estimate the averagefinancing requirements of $2.47 trillion per year--about $1.1 trillion more on averageper year over the same time period. We present results in table 2 showing the Sanders’financing plan. However we also do an analysis of the additional taxes needed to payfor the $1.1 trillion underfinancing. This would require an increase in the payroll taxfrom 6.2% to 14.3% and an increase in the income related premium from 2.2% to 5.7%-- a combined 20 percent tax on income. In light of the overall scope of the Sanders’financing proposals, additional marginal tax increases on families over $250,000 seamunrealistic. The results are presented in Table 3 This financing requirement is similarto the tax increases needed to finance the proposed Vermont single payer plan.

A single payer plan would have dramatic distributional impacts on Medicaid andMedicaid spending, and what individuals and businesses pay compared to current lawunder the Affordable Care Act. Medicare beneficiaries would no longer pay premiumsand face no sharing but would pay higher taxes. In general small businesses that donot offer insurance today with 50 or fewer workers would face a 6.2% payroll taxincrease. Low income populations living in poverty receiving Medicaid would pay morethrough the 2.2% income tax and 6.2 percent reduction in wages.