From the source of link 3:

Figure 17 Primary Reasons for Leaving Last Housing, All Participants

• Lost or reduced income: 12%
• Conflict among residents: 9%
• Didn't want to impose/wanted own space: 7%
• Conflict with property owner: 7%
• Someone else became sick, disabled, or died: 6%
• Building was sold or foreclosed: 6%
• Violence or abuse in the household: 5%
• Breakup between residents: 4%
• Participant's substance use: 4%
• Other needed more space: 4%

and also:

To understand what participants believed may have prevented their homelessness, we asked them to engage in a thought experiment about the likelihood that their homelessness could have been prevented had they received financial intervention. We provided all participants with three different scenarios and asked them whether each intervention would have prevented their becoming homeless for at least two years.29 The interventions were: (1) a monthly rental subsidy worth $300-$500; (2) a one-time payment of $5,000 to $10,000; or, (3) a voucher that limits rent contribution to 30% of their income (such as a Housing Choice Voucher).

FIGURE 21 Participant Report of Effect of Hypothetical Homelessness Prevention Interventions by Family Structure

All

• $300-$500/month shallow subsidy: 70%
• $5,000-$10,000 one-time payment: 82%
• Housing voucher: 90%

So while "not enough money" might not have been the most common cause for people being homeless, the vast majority of people think having more money or cheaper housing would have prevented them from becoming homeless.