• Compared to private elections, public elections are high stakes—the traditional values of being elected (power, money) are much lower in private elections, such as for IEEE, than in even a relatively minor public election. Hence, the motives to cheat are low. Likewise, the budgets are much smaller.
• Public elections have a long history of manipulation in nearly all countries. While there's no doubt that manipulation happens in private elections (for example, the 2013 US Rowing election), the history is not nearly so rich, largely as a result of the low stakes and lower budgets.
• The need for ballot secrecy is not nearly as strong in private elections. While it would be unusual for a professional organization to examine ballots, there's no promise that they'll be secret. If tampering were suspected, the organization could more easily verify it from voter sampling.
• Public elections often have a legal requirement for when the election must be held and the results finalized. In contrast, an association can simply delay replacement of officers—any legal issues requiring timely elections are fairly minor.
• Associations typically have a reasonably strong tie to their members. Unlike public elections in which a voter might participate infrequently (such as every four years for many US voters), association members have more of an incentive to stay in touch because they pay for membership. The result is that associations will have more accurate rosters of their members, including email addresses, than will election offices.