Governments do occasionally accept amendments proposed by the opposition. This is more likely to happen if the amendments is a sound technical improvement that doesn't have policy implications (or, in other words, that is consistent with the government's policy). Amendments proposed in order to call attention to opposition policy, or to contrast the differences between government policy and opposition policy, are most unlikely to be accepted by the government.
The bottom line is that the government decides which amendments will be taken on, and which will be rejected. The government has a cast-iron majority in both houses, so it wins all the votes.