The police know that these men escalate so why they aren't interested is...
Some escalate, some don't, some de-escalate
The nearest example of an appalling crime like this, although very different in many ways, is the crimes of Russell Williams.
He started off with voyeurism and escalated to burglary where he would steal lingerie and masturbate in women's homes through to sexual assaults and murders.
en.wikipedia.org/wiki/Russell_Williams_(criminal)
Regarding indecent exposure - I have been very distressed to have been on the receiving end of such behaviour several times, starting when I was a little girl.
I do believe it is important, however the police are under-resourced and have to triage reports of crimes and respond to those that are more serious.
Thus I understand that they will respond to a stabbing (an almost daily occurrence) in a robust way, but that this may leave them with no resources to respond to a report of indecent exposure.
People screaming "defund the police!" is not going to help. Obviously
As with the NHS vast recources have been squandered on leadership training, training from Stonewall and other allied groups, so there are a number of issues to address