While Xero and other platforms are new and shiny (not that new... xero is almost 10 years now), MYOB still commands a significant market share. However, being the incumbent is often a very difficult position because you have "baggage",
user knowledge
Loads of people have been using MYOB forever. This simple fact makes it the superior solution for many businesses. If you or your staff have an intimate understanding of a software package, then there's little incentive to switch to an alternative even if there are compelling offerings available.
User knowledge can be something of a disadvantage to the software provider as well, because it restricts their ability to change. As a key example, the MYOB UI and workflow is very much built around the concept of inputing transactions and periodically reconciling them, however with the advent and proliferation of data feeds from banks perpetual reconciliation has become a more effective and efficient approach adopted by Quickbooks, reckon one, and Xero.
accountants suite
MYOBs professional accounting package for accountants is widely used in Australia. It's probably on par with handisoft in terms of robustness, flexibility, and pricing. This is a real source of value for MYOB as accountants are more likely to encourage their clients to use MYOB as well to increase efficiencies in converting data between the client and the practice.
pre purge reporting
When you roll over a MYOB file you have the option to purge lot of the transactional data in order to save disk space and keep the data file more manageable. This should be avoided unless it's really necessary. Being able to review transactional reports from prior periods is really useful, perhaps not day to day but certainly for our accountant.
When working on a data file which has been purged, if you do need to review reports from earlier periods the only option is to find a backup file which still contains the transactional data. It's a frustrating process of digging around in backup folders and files until you find the right one.
versioning
More customers than MYOB would like to admit are still using v19 which was released in 2012. The basic problem is that at that time you could purchase MYOB with a once off license, but thereafter the licensing was subscription based. Having deprecated versions of software in popular use is a disaster for software providers, because users aren't receiving the best possible experience. In this particular case MYOB as the incumbent is already fighting off a perception that it's previous generation software. Whatever the state of their current offerings, their pricing model is encouraging this perception. When faced with a similar situation Microsoft decided to offer free upgrades. Obviously they considered that forgoing the potential income from upgraders was a lesser cost than having users stuck in old versions. That said, Microsoft didn't switch to a subscription model as did MYOB.
application programming interface
MYOB's API sucks. There's no other way to say it. Other platforms have simple, contemporary API's which are very accessible to developers. MYOB's is closed (you need to apply for access), unnecessarily complex, and completely separate (and disparate) API's are required to interact with the various versions of MYOB software in common use. This still effects users even if they've never heard the term "API", because the platform is much less accessible to programers seeking to develop third party apps and plugins. Third party apps are often developed by single person providers with extremely limited resources. When considering potential projects or roadmaps for those projects, they have to choose a path with the greatest return for the required time investment. Integration with MYOB is often deferred in favour of other platforms because developing for the MYOB API takes more time.