Why until just now the Padres have played at Rogers, both stadiums are fairly old but why hasn t it happened until now?

Because when MLB introduced interleague play in 1997, it did so in part by promoting it to doubting fans as "see every team! at last!" et cetera -- and this was, in retrospect provably, a bill of goods. It was horse droppings. Oh, the baseball powers cared about SOME matchups -- Yankees and Mets, Cubs and White Sox, the close-by regional matchups that are easy to sell to the casual fan and make for good tv ratings (albeit very short-term; three games is exciting, whereas 12 games, eh, the shine wears off quickly).

So for the marquee matches, sure, those were of interest. But San Diego-Toronto? Nah. No one cared about that, so MLB had no incentive to make it happen and, indeed, it took until now, the 20th season of interleague, before the Pods finally visited Toronto (they have played thrice before, each time in San Diego).

Interleague was a gimmick when it was introduced and MLB sold it as snake oil, which it still is. But enough vocal fans swallow this kool-ade and buy enough tickets that it is here to stay. Just don't ever expect "see every team" to really be a priority to baseball.

Rogers Center opened in the 90s and Petco Park just recently, so, actually neither stadium is old. They should last 50+ years.

Inter league play is only a few series per year. It takes time for all teams to see each other.