Primary candidates usually enter a debate only it’s in their best interests to do so. Biden has already said he will not debate any of his challengers. Trump had hinted the same.
That’s their right, of course. But it’s bad for the country. Voters should be able to hear what all the candidates say on the issues. Any candidate that declines a debate is cheating the voters.
Side problem: Most debates are, unfortunately, fixed. This can be solved by allowing each candidate to pick at least one questioner, and have veto power over any proposed moderator.
Will such reforms ever happen? Probably not.
If you want to hear Trump on the issues no problem. Read at his site, listen to his interviews and the rally speeches. Then you will be informed. Or you can watch a dog & pony show catering to one liners and false statements to “getcha”. Debates are debates in name only.