zhème hǎo de jīhuì, nǐ wèishénme bù shìshi?

Here 这么 means so, such, or this much. It is used to emphasize degree.

So 这么好的机会 means something like:

• such a good opportunity
• so good an opportunity

It shows the speaker thinks the opportunity is especially good.

的 links a modifier to a noun.

In this phrase:

• 这么好 = so good
• 机会 = opportunity
• 这么好的机会 = an opportunity that is so good

A simple way to think of it is:

modifier + 的 + noun

Examples:

• 好的老师 = a good teacher
• 便宜的东西 = cheap things
• 这么好的机会 = such a good opportunity

So 的 is there because 这么好 is describing 机会.

In Chinese, not every noun phrase needs a measure word.

Here, 这么好的机会 is a descriptive noun phrase, not a counted one. The speaker is talking about this kind of opportunity as a whole, not saying one opportunity, two opportunities, etc.

You can also say:

• 这么好的一个机会

This adds 一个 and makes the phrase feel a bit more concrete, like such a good opportunity / such a great chance. Both are natural.

So:

• 这么好的机会 = very natural
• 这么好的一个机会 = also natural, slightly more specific or emphatic

为什么不 + verb often means Why don’t you ...?

In English, Why don’t you try? is often a suggestion, not always a real request for an explanation. Chinese works the same way here.

So:

• 你为什么不试试？ can literally mean Why don’t you try?
• It often sounds like a suggestion, encouragement, or gentle push

It does not always mean the speaker is demanding a reason.

试试 is the verb 试 repeated once. This is called verb reduplication.

It often makes the action sound:

• lighter
• more casual
• less forceful
• like give it a try

So:

• 试 = try
• 试试 = try it a bit / give it a try

This makes the sentence sound more natural and less direct than a plain command.

Yes, they are very close.

Both mean give it a try.

• 试试
• 试一试

These are often interchangeable in everyday speech.

Very roughly:

• 试试 sounds compact and conversational
• 试一试 can sound a little fuller or slightly more deliberate

In this sentence, both work:

• 你为什么不试试？
• 你为什么不试一试？

Yes, 你 can be omitted if the context is clear.

Chinese often leaves out subjects when they are obvious.

So both are natural:

• 这么好的机会，你为什么不试试？
• 这么好的机会，为什么不试试？

Including 你 makes it more directly aimed at the listener. Omitting it can sound a little smoother or less pointed, depending on tone.

The comma separates the topic from the main comment.

• 这么好的机会 = as for such a good opportunity
• 你为什么不试试？ = why don’t you try?

This kind of structure is very common in Chinese. The speaker first brings up the situation, then comments on it.

You can think of it like:

• With such a good opportunity, why don’t you try?
• As for such a good opportunity, why not give it a try?

The comma helps show that pause.

It is often more like advice, encouragement, or persuasion.

Even though it is in question form, the speaker is usually not just asking for information. They are often implying:

• You should try
• It would be a pity not to try
• This is a great chance

So the emotional meaning can be stronger than the literal wording.

这么好的机会 is usually more expressive than 很好的机会.

• 很好的机会 = a very good opportunity
• 这么好的机会 = such a good opportunity / so good an opportunity

这么 often suggests the speaker is reacting emotionally to the situation. It can sound like:

• This chance is really so good!
• An opportunity this good!

So 这么好的机会 feels more vivid and persuasive.

Normally 不 is fourth tone: bù.

But before another fourth-tone syllable, it changes to second tone: bú.

Since 试 is fourth tone (shì), 不试试 is pronounced:

• bú shìshi

This is a very common tone change rule in Mandarin.

Yes. In context, both are fine.

Possible natural translations include:

• Why don’t you give it a try?
• Why not try?
• With such a good opportunity, why not give it a shot?

Since the meaning is already known, the key point is that 为什么不试试 is a very natural Chinese way to make a suggestion.

Usually yes, but in everyday speech it can also feel close to chance.

So 机会 can be translated as:

• opportunity
• chance

In this sentence, 机会 is a favorable situation that the listener could make use of. So opportunity and chance both work well.