Anecdotally, I've found it difficult to persuade potential employers that I won't just quit after six months and start another business. It's a legitimate concern on their part - if you're someone who likes the challenge and (potential) reward of running your own business then you're less likely to stay in a salaried job for as long as someone else. Employing someone should really be a long term commitment from both parties.
Secondly, it's quite hard if you failed. I learnt a huge amount about running a company, building software, even about who I am, when I've been doing startups, but ultimately the main thing I've demonstrated is that I can put a lot of time and energy in to projects that fail. I didn't have the insight to change what needed to change to ensure success or to walk away earlier to limit my losses. Those aren't great things to show people.
All in all, being self-employed does make it harder to get a job afterwards. If you recognise why though, you can defend yourself against those issues that employers will have.
On a more optimistic note, from an employer point of view, I would prefer if you had made some mistakes in the past on your own funds, and hopefully, learned a good lesson in the process, and would not reproduce them with the company money.
If "employing someone should really be a long term commitment from both parties," then employers need to start treating it as such again. Right now this is simply one among many, many imbalances between employees and employers: the loyalty demand is, in my view, a one-way street.
Employees are not to expect long-term loyalty style commitments from employers these days. Training, retirement investment packages, career paths and other intangibles that make a long-term commitment at a single employer potentially a good move don't exist anymore (at least not in any significant numbers).
Long-term investment with a single employer carries risks for the employees: opportunity costs, skill stagnation or over-specialization, far lower long-term compensation without internal "job hopping" up the management ladder (and even then it's not nearly the risk-free move it was even 20 years ago, let alone 30 or 40), etc. Employers don't acknowledge these risks the employees take, though, and simply demand loyalty without wanting to make an investment of their own other than a begrudgingly given compensation package (that is often below the actual value an employee provides).
Of course it's not fair; and that's just the way it is--it's something serial entrepreneurs and "job hoppers" should just be prepared to deal with.
Secondly, it's quite hard if you failed. I learnt a huge amount about running a company, building software, even about who I am, when I've been doing startups, but ultimately the main thing I've demonstrated is that I can put a lot of time and energy in to projects that fail. I didn't have the insight to change what needed to change to ensure success or to walk away earlier to limit my losses. Those aren't great things to show people.
All in all, being self-employed does make it harder to get a job afterwards. If you recognise why though, you can defend yourself against those issues that employers will have.