It is extremely annoying to have to complete a second reCaptcha to be told one have to wait 45s more seconds before doing it again, for a third time!!!
Any potent administrator would do every means to keep his forum safe under any circumstances and the moment one control is weak or not achieving the intended objective, another one is put in place and that's exactly what is going on here and even at any point in time when this one is not enough and there is need to always do email activation, it will be implemented and you will be forced to comply if you still want to be welcomed into the forum.