Why might a technical job post require a number of LinkedIn followers?

The bosses nephew has 120 followers on LinkedIn. Since the boss wants his nephew to get the job, they add “more than 110 LinkedIn followers” to the requirements, so half the candidates don’t meet the criterion, and the other half sees it as a red flag.

[Most beneficial possible interpretation]

It may be because the consulting / networking aspect of that ERP consulting position is larger than you expect, aka it's not an as purely technical job as you(r question title) suppose.

In that case it's a kinda weird but easy to track way of filtering applicants for a baseline of networking skills / habit.

Whether it's a good metric is a wholly different question, but that's my attempt at a benign reading for this unusual requirement.

There is another alternative explanation which came to my mind when I saw this question when it was first asked and I have now found some substantiation that I can use to answer.

Basically, one subject that has cropped up more and more in the malware/infosec news these days is the risk of mistakenly hiring North Koreans IT workers posing as regular remote workers. These people can then either a) transfer their salaries to North Korea, to circumvent sanctions or b) steal your IP or install malware. Sometimes both.

And it turns out that one easy metric is the lack of a normal-looking LinkedIn profile.

Fake North Korean IT workers: How companies can stop them • The Register

Over the past few months, Socure has seen a ton of fake candidates applying for open jobs, according to Little, who has been leading the charge on the IT worker scam front. This seems an especially ironic choice for employment scammers, because Socure provides identity verification services to other companies

Chief among these disconnects were "shallow" LinkedIn profiles paired with "beefy resumes," she explained, citing job-seeker claims of working at Meta, attending Ivy League schools, developing major tech companies' flagship products … but then only having 25 LinkedIn connections.

Keep in mind how difficult it would be to seed a profile with connections that organically link to other connections that hold up under scrutiny.

This isn't to put down the other answers. They may still apply in many/most circumstances, up to you to evaluate your context.