Someone has to manually apply handicap strokes, hole by hole. A proper stroke allocation isn't "subtract the handicap from the total" — it's stroke index by stroke index, one stroke on a player's hardest holes, a second stroke kicking in only past 18. Almost nobody builds that formula correctly on the first try, and almost nobody rebuilds it correctly for every game running that day (a low-net game and a match-play nassau don't even use strokes the same way). It usually gets approximated, and the approximation is where the arguments start.
Live updates require everyone to actually refresh. A spreadsheet isn't really "live" unless everyone has the tab open and keeps hitting refresh, and even then it's a grid of numbers, not a scorecard anyone would call fun to look at mid-round. Nobody not currently playing is casually checking in on it from their phone in the clubhouse.
A phone screen doesn't fit a full scorecard grid. Eighteen holes times however many players times however many side games is a wide grid. On a laptop that's readable. On the phone that's actually in your pocket on the course, it's a horizontal-scrolling mess, tiny text, and mis-tapped cells. Golf betting happens on the course, on a phone, one-handed, between shots — the exact environment a spreadsheet handles worst.
Math errors are common and undetectable until someone disputes it. A dragged formula that didn't update, a copy-pasted row that broke a reference, an autocomplete that changed a cell reference — any of these silently produces a wrong number, and nobody notices until the 19th hole, when someone says "wait, that's not right" and now the whole group is re-deriving strokes on a cocktail napkin. The sheet doesn't show its work in a way that's easy to audit under pressure.
There's no live view for people not playing. If a spouse, buddy, or the guy who couldn't make it wants to follow along, there's nothing to send them that's actually watchable — at best a read-only link to a spreadsheet, which is exactly the "grid of numbers" problem above.