First, states are allowed to make their own election laws.
Second, that said, it doesn't inherently mean that such laws would be constitutional -- nor that they wouldn't be -- just that there would likely be a court challenge.
Third, all 14 states are solidly Democratic so even if the bills passed and were constitutional, it most-probably wouldn't affect the results of the presidential election, and therefore wouldn't seem to be anything that would prompt Trump to release his tax returns.
Fourth, there were five other states that previously had a similar bill, and it failed to pass in all five states, although none would be considered "strong" Democratic -- Maryland, Mississippi, New Hampshire, New Mexico and Virginia.
Fifth, just because such a bill wouldn't likely affect the presidential race, it could conceivably impact the races within the state for Senate, House and local. If there was no presidential candidate for a party on the ballot to vote for, it's possible that that would keep any appreciable number of members of that party at home. Or not.
And sixth, it would seem that if such a bill did pass in these states and was upheld that it would become a major campaign issue for Trump and rile up his base. On the other hand, that would have most of an impact in red states where Trump was most-likely to win, and in blue states where the bill was law, Trump wouldn't be on the ballot so no matter how riled up anyone was...they couldn't vote for him.
At the moment, this is of course nothing but rumination. But it's not theoretical since the bills do exist and will be voted on.