Recruiting is tough. Thinking about my last job transition, there was probably a golden period of two weeks where I was truly open to all recruitment possibilities. By the end of those two weeks I was starting to move into the offer stages. So realistically I can't blame the frequency and volume of recruitment communication; it's possible a followup message would have struck at exactly the right moment.

That being said, for senior engineers surely it's more likely that recruitment will be more driven by referrals by trusted colleagues? I don't think I've seen referral bonuses rising at a commensurate rate.