I would look to complacency and/or stupidity as a primary factor in localised spikes.
In Australia we were looking pretty good when it came to beating the virus into submission. We had very little community transmission because most of our cases were in people coming home from overseas and after a mishandled situation of passengers from the Ruby Princess, quarantining in hotels was working fairly well.
Then comes the stupidity. In Melbourne the government contracted a private firm to supervise quarantining. They then subcontracted to another security firm and from there it went to hell. The men who were supposed to be keeping the people isolated were not doing their job. They fraternised pretty freely, eating with them and in some cases having sex with the people they were supposed to be guarding. They didn't use PPE or masks.
Needless to say, they became infected, took it home to their families and into the community. Melbourne started finding active cases scattered throughout a number of suburbs with a cluster in some public housing towers. Last week these towers were placed into hard lockdown for 5 days to allow the authorities to test everyone inside. One tower was perfectly clear, others had a few active cases and these people are now in quarantine and one tower had 25% infection rate. This one will remain under hard lock down for at least another week with repeated testing to see how the situation develops.
Knock on effects are tough. The Victorian border is now closed and only people with a genuine need to travel are allowed to cross in either direction. We were ready to ease restrictions relating to social distancing but this has been slowed because there have been blatant examples of people throwing caution to the winds, congregating in and outside venues. We have also had a few BLM protests but the organisers have been pretty responsible, providing hand sanitisers, face masks and urging social distancing. Much more responsible than this situation outside a venue in Double Bay, Sydney a couple of days ago. Double Bay is a high priced suburb in the eastern suburbs. A very different demographic to the public housing towers in Melbourne.
These people are putting their own pleasure ahead of everyone elses' health and the people whose businesses are suffering but as always there are others who are going out of their way to be part of the solution rather than part of the problem.
These people are members of the Somali community who have organised themselves to provide food and other necessities to people in the locked down towers. They are all volunteers. The Sikh community is also present providing free meals to the police and medical teams.
The only way to beat a viral pandemic is to pull together through the tough times. Acting selfishly, demanding one's right to personal freedom when asked to surrender some of it is a pathway to economic and health disaster. Sometimes we have to consider extraordinary measures such as closing borders that not have been closed for over a century. And we have to look after each other until it is over.