I don't know any of the details of this case, but I find it very surprising. I have heard from a very senior person in the Rabbinate who has personally worked on all the open cases of gett refusal that:

- Under the current chief Rabbis, there has been a dramatic shift to put pressure on gett refusers, and the Rabbinate will use everything in it's power to help Agunot, including confiscating passports and drivers license, sanctions at work when possible, and if necessary prison. This was not the case with the previous chief Rabbis.

- There have been more cases of women refusing to accept getts than of men refusing to grant getts, however in the majority of cases involving women refusing to receive a gett, they are normally resolved with the threat of sanctions. Often women refuse to accept a gett as they are angry with a husband who had an affair, and want to stop him marrying his mistress, however when threatened with confiscation of their drivers license they often back down (therefore most long-term gett refusers are men)

- Heter Meah Rabbonim is almost never used in Israel. The only exception is if there is a physical reason why the woman cannot accept a gett (for example she is in a long-term coma)

As I said, I know nothing about this particular case, but Heter Meah Rabbonim is extremely rare through the Rabbinate in Israel (I don't know if private Batei Din such as the Eida Charedit have a different policy)

there was just another case of hetter mea rabbonim being used by a rosh yeshiva. He just got engaged the other day (I forget his name but I saw an article somewhere about it). His [previous] wife has been in a coma.

the story is a bit strange, but this woman has gotten the reputation as being strong and vengeful. She was abusive in the relationship (allegedly), and perhaps their attempts to intimidate her were unsuccessful and they saw it would not lead to anything. I dont know

"The truth is I never understood how the hetter mea rabbonim gets around the bigamy issue in western societies that have laws against bigamy and polygamy."

This is actually quite easy in most countries. You just get a secular divorce. In the eyes of the secular law, you are now divorced and free to remarry. That the Torah still considers you married makes no difference.

Of course, that would not work in Israel, which only has religious marriage and divorce.

It can also sometimes lead to unusual complications. There was a case in Monsey a while back (maybe 20 years) where a man got a secular divorce from his wife, but refused to give her a get. He then remarried another woman. The Va'ad Harabonim of Great Monsey protested this flagrant breach of halacha. So he sued them for libel! The secular court ruled that this was purely a religious dispute, over which the First Amendment forbids secluar courts from resolving.

You can read the court's opinion, and all the background, here: https://casetext.com/case/klagsbrun-v-harabonim