They are not the same thing. Trump was not known to be at the end of his term and they had the Senate. Obama lost the Senate and was about to leave office. Again, at the time they rejected Garland, it was widely believed that Clinton was going to be the next president. Trump was the GOP front-runner by then and no one believed he was a serious threat to win. McConnell & co refusing Garland on their stated grounds was a case of actually staking a principle, even at greater risk to their interests, as many Democratic pundits gleefully pointed out at the time, certain that Hillary was going to ram a worse (from the Republican point of view) nominee down their throats in 2017. Voting Garland down would have been mere partisanship. Even if their motives for what they actually did were partisan, they still did so over a principle that applied both ways and would have benefitted the Democrats had they won the election. As it was, in 2020, it was possible that Trump was going to win, and seen as likely, hence the disbelief at the outcome (I posted at the time how unusual his defeat was against so many factors), and furthermore, the Republicans seemed likely to retain control of the Senate. As it was, Trump's high-handed and self-serving attempts to claim Georgia's electoral votes probably cost the Republicans both Senate seats in the post-election runoff, and control of the Senate with them.

The motive for "pushing Barrett through" before the election was that voters were disappointed with Trump and he needed a win. Some people were talking about a delay in the appointment as an effort to hold the nomination hostage to a Republican turnout. There was already a sense that Trump was taking the base for granted, and leaving the SCOTUS open until after the election might have been perceived as a deliberate tactic, saying "vote for me, or a Democrat is going to fill that seat instead..." Or maybe McConnell had repented and taken to heart the Democrats' assertions that it's 100% on the President and the Senate should just shut up and do what he says.