Why is "purchase" pronounced the same as a verb and as a noun, unlike other words such as increase? [closed]

Solution 1:

There are examples of the word with its second syllable stressed. These two are from c.1380 and c.1420.

Chaucer: Canterbury Tales. Prologue:

With grene trees shadwed was his place.
He koude bettre than his lord purchace.

The Castle of Perseverance:

Have here, Mankynd, a thousend marke.
I, Coveytyse, have thee this gote.
Thou mayst purchase therwyth bothe ponde and parke

We are losing the distinction you mention between nouns and verbs.

proTESTers have become PROtesters who PROtest against things.
Goods are regularly EXported, rather than exPORTed.
ATT-ribute is replacing At-TRIB-ute
CONflict is ousting ConFLICT
EXport, IMport and TRANSport are supplanting exPORT and imPORT and transPORT, but we do still dePORT people.
Only surveyors surVEY: everyone else seems to SURvey.