Why was switch migration stopped?

[Maygikal]

Title says it all, why would switch migration be stopped? I have searched for reasons why to no avail. Some people, such as myself, didn't own a switch during the migration period and as such couldn't migrate their data.

[WhiteMarker]

Because that's how these migrations worked.

They took place after Warframe's release on a new platform. That way the new platform got populated quickly by people who knew what to do. These "high level" players could then help the new players.

DE announced the upcoming switch-migration a long time before it took place. It was up for quite some time. And then they announced the ending of said migration a few weeks before it ended.
Long story short: There was enough time to get a Switch and migrate.

If you want to play on the Switch, you can easily start a new account.

[Letter13]

Also, the console manufacturers did not want to allow migrations to go on forever, and in some cases they did not want migrations to occur at all (mainly because migrations were at first viewed as a potential loss of revenue on micro-transactions to the console makers; i.e. if a player who had bought a whole lot of items with platinum migrated to console, then the console maker would not have profited from the player having bought that platinum to buy those items).

DE was able to convince Sony to allow migrations for a limited time. Microsoft also allowed migrations (so that XB1 players would not be excluded from the same opportunities as PS4 players).

For Nintendo Switch, regardless of how long Nintendo would have been alright with migrations occurring, there is an issue of fair and equal treatment; if Nintendo allowed DE to keep migrations going forever, that would be unfair and unequal treatment were DE to then implement migrations forever, and would give Nintendo Switch players more preferential treatment. 

Long story short, if you want permanent migration opportunities not limited by time on one platform, then such a thing needs to be available for all platforms--this way all console players regardless of their platform of preference have equal opportunities to migrate--which is what has occurred. Each console received a temporary migration period where console players could migrate their PC data to their console account. The only way another migration would be implemented is if all 3 console makers agreed to allow a second (or third/fourth/permanent) migration window.