People are not voting Labour because they have been told that the leader of the party is incapable of being PM and he can't lead the opposition party and raise support, which is what you would expect a nasty opposition to communicate via the media sources they can influence, eg right wing press and the BBC.
The right wing media tell us that Corbyn is in way over his head and that there isn't the confidence in him to lead the country and through Brexit negotiations. If the Conservatives were more confident in this statement, they would give him more balanced converage - they traditionally support and are fairer to weaker labour leaders. They try the double bind bullshit here 'We need a strong opposition' Yeah bullshit! they need a weakened perception of opposition, and you are buying it.
People might disagree and dislike May but there is no doubt who we are being told is the more intelligent and professional of the two and who is the more capable, even though she is flip flopping and talking in complicated delusions (which works, sadly, because if challenges to them are not publicised and May won't debate with Corbyn publicly, uncritical thinkers just buy it).
If labour had a leader that was up to the job they would be attacked ruthlessly and relentlessly the Tories, undermined, devalued and ridicules as much and as often as possible for fear that people might hear that strength. The Tories are taking advantage of their access to and support of the right wing media to attempt to undermine his messages before they are heard, and to limit the chances of them being heard. Corbyn and those who have backed him are using this time out of the spotlight to strengthen and consolidate his position.
The fact that they are still scared, even with the gift to May that is the SNP taking a chunk of labour consituencies out of the mix, shows how weak the Tory party really are under all their bravado.