I repeat asking about "g" > "k", "d" > "þ", "b" > "p", "k" > "h", "t" > "þ"  alternation in Germanic languages

Old English growan Russian (со)зревать  Gothic  ---
Old English corn   Russian зерно        Gothic kaurno


Old English teran Russian драть         Gothic (ga)tairan
Old English þorn Russian тёрн           Gothic þaurnus

I mean,

If Old English corn and growan are cognate

Why are Old English teran and þorn not cognate?